reaction rates - الرئيسية

Germanium

32

Ge 72.61

Nickel

28

Ni 58.693

Uranium

92

U 238.029

Sulfur

16

S 32.066

REACTION RATES Worksheets

Chemistry worksheets, Reaction Ratees

pg. 1 http://chemya.weebly.com

Chemical Reaction Rate Chemical reactions vary widely in the speeds with which they occur.

➢ Some reactions occur very quickly. If a lighted match is brought in contact with lighter fluid or

another flammable liquid, it erupts into flame instantly and burns fast.

➢ Other reactions occur very slowly. A container of milk in the refrigerator will be good to drink

for weeks before it begins to turn sour.

➢ Millions of years were required for dead plants under Earth’s surface to

accumulate and eventually turn into fossil fuels such as coal and oil.

Chemists need to be concerned with the rates at which chemical reactions

occur. Rate is another word for speed. If a sprinter takes 11.0 s to run a 100 m

dash, his rate or speed is given by the distance traveled divided by the time.

speed= 𝐝𝐢𝐬𝐭𝐚𝐧𝐜𝐞

𝐭𝐢𝐦𝐞 =

𝟏𝟎𝟎 𝐦

𝟏𝟏.𝟎 𝐬 = 9.09 m/s

1) why we use the word rate to express the speed?

We say that it is his average rate because he did not run at that speed for the entire race.

Reaction rate is the change in concentration of a reactant or product with time.

2) Conclude the units for reaction rate.

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Suppose that a simple reaction were to take place in which a 1.00 M aqueous solution of

substance A was converted to substance B.

A(aq) → B(aq)

Suppose that after 20.0 seconds, the concentration of A had dropped from 1.00 M to 0.72 M as A was

slowly being converted to B. We can express the rate of this reaction as the change in concentration

of A divided by the time.

Rate = 𝐪𝐮𝐚𝐧𝐭𝐢𝐭𝐲

𝐭 = −

[𝐀]

𝐭

3) What does the bracket around a symbol or formula means?

A bracket around a symbol or formula means the concentration in molarity of that substance.

4) why do we use negative sign if we calculate the ate using the change of reactants concentration?

The change in concentration of A is its final concentration minus its initial concentration. Because the

concentration of A is decreasing over time, the negative sign is used. Thus, the rate for the reaction is

positive.

Rate =− [𝐀]

𝐭 = −

𝟎.𝟕𝟐 𝐌−𝟏.𝟎𝟎 𝐌

𝟐𝟎.𝟎 𝒔 = 0.014 M/s

The molarity of A decreases by an average rate of 0.014 M every second.

quantity = change in quantity of a substance.

t = change in time. Rate = quantity

t

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Reaction rates are determined experimentally by measuring the concentrations of reactants and/or

products as an actual chemical reaction proceeds. Reaction rates cannot be calculated from balanced

equations.

5) Calculate the reaction rate for the reaction CO(g) + NO2(g) → CO2(g) + NO(g)

If the concentration of (NO) was 0.010M after 2 seconds.

6) Calculate Average Reaction Rates In a reaction between butyl chloride (C4H9Cl) and water, the

concentration of C4H9Cl is 0.220M at the beginning of the reaction. At 4.00 s, the concentration of

C4H9Cl is 0.100M. Calculate the average reaction rate over the given time period expressed as moles

of C4H9Cl consumed per liter per second.

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7) Use the data in the following table to calculate the average reaction rates.

Experimental Data for H2 + Cl2 → 2HCl

Time (s) [H2] (M) [Cl2] (M) [HCl] (M)

0.00 0.030 0.050 0.000

4.00 0.020 0.040

1. Calculate the average reaction rate expressed in moles H2 consumed per liter per second.

2. Calculate the average reaction rate expressed in moles Cl2 consumed per liter per second.

3. If the average reaction rate for the reaction, expressed in moles of HCl formed, is 0.0050 mol/L·s,

what concentration of HCl would be present after 4.00 s?

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[NO] at t1 = 0.000M [NO] at t2 = 0.010M t1 = 0.00s t2 = 2.00s

Rate = [𝐍𝐎]

𝐭

Rate = 𝟎.𝟎𝟏𝟎𝐌−𝟎.𝟎𝟎𝟎𝑴

𝟐.𝟎𝟎𝐬−𝟎.𝟎𝟎𝒔 = 0.0050 mol/(L.s)



Collision Theory

8) Define collision theory.

Collision theory is a set of principles that states that the reacting particles can form products when

they collide with one another.

9) What are two requirements for collision to form a product?

1. The collisions have enough kinetic energy

2. and the correct orientation.

collisions (a,b, and d) is called an ineffective collision, collision(c) is called an effective collision.

10) Two molecules collide and then bounce off of one another. Explain why?

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Activation Energy

Why do some chemical reactions occur readily while others require input of heat in order to take

place? If we mix metallic sodium with water, a reaction occurs immediately, releasing a great deal of

heat. Group II metals, such as calcium, react at a much slower rate.

Activation energy for a reaction is the minimum energy that colliding particles must have in order to

undergo a reaction.

11) Why do some chemical reactions occur readily while others require input of heat in order to take

place?

Some reactions occur readily at room temperature because the reacting particles already have the

requisite activation energy at that temperature. Other reactions only occur when heated because the

particles do not have enough energy unless an external source of heat provides the particles with

more kinetic energy.

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Potential Energy Diagrams

The energy changes that occur during a chemical reaction can be shown in a diagram called

a potential energy diagram, or sometimes called a reaction progress curve.

Potential energy diagram shows the change in potential energy of a system as reactants are

converted into products.

Endothermic reaction Exothermic reaction

The total potential energy of the system increases

The total potential energy of the system decreases

System absorbs energy from the surroundings System releases energy to the surroundings

The energy of the products is greater than the energy of the reactants

The energy of the products is lower than the energy of the reactants

The activation energy for a reaction is illustrated in the potential energy diagram by the height of the

hill between the reactants and the products. For this reason, the activation energy of a reaction is

sometimes referred to as the activation energy barrier. Reacting particles must have enough energy

so that when they collide they can overcome that barrier.

The activation energy (Ea) of a reaction is the barrier that must be overcome for the reactants to be

able to become products, so if,

A. The activation energy is low, meaning that the reaction is likely to be fast.

B. The activation energy is high, meaning that the reaction is likely to be slow.

12) In an endothermic reaction, is the potential energy of the products higher or lower that the

potential energy of the reactants?

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13) In an exothermic reaction, is the potential energy of the products higher or lower that the

potential energy of the reactants?

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14) What does activation energy tell us?

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Activated complex

Reactant particles sometimes collide with one other and yet remain unchanged by the collision. Other

times, the collision leads to the formation of products.

Activated complex: The state of the particles that is in between the reactants and products .

An activated complex is an unstable arrangement of atoms that exists momentarily at the peak of

the energy barrier. Because of its high energy, the activated complex exists for an extremely short

period of time (about 10−13 s). There is equal likelihood that the activated complex either reforms

the original reactants or goes on to form products.

15) Do all collisions of reactant particles lead to products?

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16) Explain collision theory.

Collision theory is a way to explain why different reactions occur at different rates.it states that for a

reaction to occur, particles need to collide with enough energy and hit with the correct orientation.

17) What are the two things that must take place in order for a reaction to take place between

molecules or atom?

Particles must have a collision with enough energy and the correct orientation.

18) Explain why all reactions have activation energy, using your knowledge of collision theory.

According to the collision theory, all reactions must have a collision. Collisions must occur with

sufficient energy. No chemical process can take place without having at least a little energy to get

things started.

19) Describe how the activation energy of a reaction affects the overall rate of the chemical reaction.

The higher the activation energy, the more energy is required during the collision for the reaction to

occur.

20) Explain the difference between high and low activation energies and how this affects the reaction.

The higher the activation energy, the more energy the particles will need when they collide. If the

activation is low, reactions tend to occur faster then higher activation energy.

21) What is a catalyst? Explain how a catalyst will speed up a chemical reaction.

A catalyst is part of the reaction that lowers the activation energy.

22) Why does increasing temperature speed up a chemical reaction? Use collision theory to explain

your answer.

Particles collide more often and collide with more force then before

23) It has been observed with one variety of paint that the rate of paint drying can be drastically

increased by adding a small amount of “accelerant”. Based on what you know of catalysts, is it

reasonable to think of this accelerant as being a catalyst? Explain.

No, accelerants are consumed during reactions. Catalysts only make them faster.

24) Use collision theory to explain why reactions should occur more slowly at lower temperatures.

When temperature is decreased there are fewer collisions and less energy

25) How can you tell which graph is endothermic and which one is exothermic? Describe your

reasoning.

✓ If reactants have more energy = exothermic

✓ if products have more energy = endothermic



26) Summarize the 3 parts of the collision theory

✓ must collide

✓ with enough energy

✓ correct orientation

27) This is an effective collision. It does react. State 2 reasons why.

• Hit with enough energy

• Hit with correct orientation

28) The following collisions do not react. State why.

a.

• Incorrect orientation

b.

• Incorrect orientation

c.

• not enough energy

29) Draw label an endothermic and exothermic graph. Make sure you include the products, reactants,

activation energy, and activated complex.

Endothermic reaction Exothermic reaction



Factors Affecting Reaction Rates By their nature, some reactions occur very quickly, while others are very slow. However, certain

changes in the reacting conditions can have an effect on the rate of a given chemical reaction.

The Nature of Reactants

Concentration

An increase in the concentration of one or more reacting substances results in an increase in the rate

of reaction. When more particles are present in a given amount of space, a greater number of

collisions will naturally occur between those particles. Since the rate of a reaction is dependent on

the number of collisions occurring between reactants, the rate increases as the concentration

increases.

In the picture, the candle on the left is burning in air, while that

one on the right side is covered by a tube containing only oxygen.

30) Describe why that one the right side has a larger brighter

flame.

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Copper

✓ when placed in aqueous

silver nitrate solution it

reacts to form silver

metal and aqueous

copper (II) nitrate

✓ Less silver formed

✓Metals

✓ Have similar

physical

properties

because of

their relative

positions of

the periodic

table

Zinc

✓ when placed in aqueous

silver nitrate solution it

reacts to form silver

metal and aqueous zinc

nitrate

✓ More silver formed

✓ The reaction of zinc with silver nitrate occurs faster

✓ zinc is more reactive with silver nitrate than copper





Surface Area

Reaction of oxygen with the same mass of iron but different shapes

red-hot chunk of steel red-hot bundle of steel wool

Reaction rate Much more slowly Faster

surface area less surface area more surface area

Collisions oxygen molecules collide with

less iron atoms per unit of time

oxygen molecules collide with

many more iron atoms per unit

of time

31) What is the relation between surface area and reaction rate?

Increasing the surface area of a reactant speeds up the rate of reaction by increasing the collision

rate between reacting particles.

Temperature

Increasing the temperature of a reaction increases the number of effective collisions between

reacting particles, so the reaction rate increases.

32) Why does food spoil faster outside the refrigerator?

Increasing the temperature increases the speed of the reaction.

Raising

the tempe

rature of

a chemical

reaction

When the

reactant

particles

are

heated

they

move

faster

and

faster

This results

in a greater

frequency

of

collisions

so

the reaction

rate increases

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From the corresponding graph,

33) How does the reaction rate change by increasing the

temperature by 10 degrees?

The reaction rate almost doubled with each increase in

temperature by 10 ° C (Kelvin)

34) Determine the relative rate of the reaction at 325K.

20

The corresponding figure shows the number of particles

versus the energy they possess during a chemical reaction

35) How do you know the number of particles may participate

in the reaction?

The area below the curve reflects the number of those

particles.

36) How do you know the number of particles that have an

energy equal to (A)?

We draw a line from point A and determine the number of particles from the vertical line.

37) How do you know the number of particles that have energy less than (A)?

Calculates the area under the curve before point (A).

38) How do you know the number of particles that have energy more than (A)?

Calculates the area below the curve after point (A).

39) How do you know the number of molecules that have greater energy than Ea?

Calculates the area below the curve after the line extending from the activation energy and

intersecting the curve.

The corresponding figure shows the same relationship but in

two different temperatures.

40) Which of the two cases, is the reaction occur at a higher

temperature?

curve T2

41) Which of the two curves has a larger total area below it?

And why?

The area under the curves is the same because the area under the curve reflects the number of

molecules of the reactants, the number of molecules is constant in both cases, even if the

temperature change.

42) Which of the two curves expresses the greater number of particles entering the reaction?

reaction in the case of a higher temperature (T2) because the area under the curve after the activation

energy (shaded area) is greater in the case of the reaction at the higher temperature (T2).



43) Which is the fastest reaction? discuss using the graph.

The reaction occurs faster at the higher temperature (T2) because the number of particles that possess

energy is equal to the activation energy or above at the temperature (T2) is greater than that at (T1)

because the area after the activation energy in the case of (T2) Curve in case (T1).

44) How do the shaded areas compare?

The number of high-energy collisions at the higher temperature, T2, is greater than the number at the

lower temperature, T1 . Therefore, as the temperature increases, more collisions result in a reaction.

Catalysts and inhibitors

A catalyst is a substance that increases the rate of a chemical reaction by lowering the activation

energy without being used up in the reaction.

With a lower activation energy barrier, a greater percentage of reactant molecules are able to have

effective collisions and the reaction rate increases.

Catalysts are extremely important parts of many

chemical reactions. Enzymes in your body act as

nature’s catalysts, allowing important biochemical

reactions to occur at reasonable rates. Chemical

companies constantly search for new and better

catalysts to make reactions go faster and thus make

the company more profitable.

45) Does the catalyst increase the amount of the products? If Not, what is its job?

A catalyst does not yield more product, its just make it produced faster.

When writing a chemical equation, where do we indicate the catalyst?

Inhibitors

Unlike a catalyst, which speeds up reaction rates, an inhibitor is a substance that slows down, or

inhibits, reaction rates. Some inhibitors prevent a reaction from happening at all.

46) How inhibitors work?

➢ Some block lower energy pathways and thus raise the activation energy of a reaction.

➢ Others react with the catalyst and destroy it or prevent it from performing its function.

➢ In biological reactions, an inhibitor might bind the enzyme that catalyzes a reaction and

prevent the reaction from occurring.

In the food industry, inhibitors are called preservatives or antioxidants. Preservatives are safe to eat

and give food longer shelf lives.






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Types of catalysts

heterogeneous catalyst homogeneous catalyst

catalyst exists in a physical state different than

that of the reaction it catalyzes

catalyst that exists in the same physical state as

the reaction it catalyzes

The reactions within a catalytic converter that convert harmful exhaust gases to acceptable

substances.

✓ Nitrogen monoxide is converted to nitrogen and oxygen.

✓ Carbon monoxide to carbon dioxide

✓ Unburned gasoline to carbon dioxide and water.

The most effective catalysts for this application are transition metal oxides and metals such as

rhodium and platinum.

47) The catalysts in pervious case are called heterogeneous catalysts. Why?

Because the catalysts in a catalytic converter are solids and the reactions they catalyze are gaseous.

48) Give each of the factors that affect the rate of reaction and then explain why they affect

reaction rate Factor Reason

concentration

The higher the concentration, the more collisions occur therefore the faster the

reaction.

temperature The higher the temperature, the faster the molecules are moving therefore the

faster the reaction.

surface area

The more surface area the more places for collisions to occur therefore the

faster the reaction

nature of

reactants

Some reactants tend to react faster than others due to many factors

catalyst A catalyst speeds up a chemical reaction without effecting the

products or the reactants.



Plotting this data in a graph, as shown below, we find that after all the acid is used up, no more gas is

evolved and the volume reading of the syringe stays constant (at volume M).

❖ Repeating the experiment starting with the same amount of acid and zinc, but warming the acid

solution, curve B will be produced. This shows a faster initial and overall rate of reaction because

B reaches level M sooner than curve A did.

❖ Starting with the same amount of acid but using powdered zinc instead of lumpy zinc, results in

curve C.

❖ Curve D shows the reaction rate when powdered zinc is reacted with warm acid.

❖ We can make the reaction go quicker still (E) by using concentrated and warm acid with powdered

zinc.

Note that each curve shows the same final volume (M) of hydrogen produced. Each curve differs from

the others only in the time that it takes to reach the final volume M.



Tick the box next to the correct answer.

49) The rate of reaction between hydrochloric acid and marble chips can be increased by:

cooling

stirring

using larger chips

using less hydrochloric acid

50) The rate at which ethanol can be produced from a fermenting mixture depends upon the:

i amount of yeast in the mixture

ii amount of sugar in the mixture

iii temperature of the mixture

i and ii

i and iii

ii and iii

i, ii and iii

51) Zinc reacts with sulphuric acid according to the equation: Zn(s) + H2SO4 (aq) ZnSO4 (aq) + H2 (g)

If we add a catalyst, it speeds up the reaction. Which of the following graphs correctly shows the

results of the reactions, one without a catalyst W and one with a catalyst C?

52) Increasing the concentration of reactants will increase the rate of a chemical reaction because:

the reactant molecules are moving faster

there are more collisions of reactant molecules

the solution is more concentrated

there is more space for reactants to react

53) Decreasing the temperature of a chemical reaction will decrease its rate of reaction because:

the reactant molecules are moving more slowly

there are fewer solvent molecules present

there is less space for the reactants to collide

the reactants are less soluble



54) The graph shows the rate of reaction in which CO2 is produced at 60°C, without a catalyst. Sketch

onto this graph two curves:

a- One for this same reaction carried out at 30°C, with no catalyst; label it L.

b- Sketch another for the reaction carried out at 60°C, with a catalyst; label it C.

55) Magnesium was reacted with an excess of dilute hydrochloric acid as shown by this equation:

Mg (s) + 2 HCl (aq) H2 (g) + MgCl2 (aq)

The volume of hydrogen produced was measured at timed intervals and gave the following results:

Volume of H2

produced (cm3) 0 7 14 19 23 26 31 38 40 40 40

Time (min) 0 0.5 1.0 .5 2.0 2.5 3.0 4.0 5.0 6.0 7.0

How much hydrogen was produced during:

▪ the first minute? ________________

▪ the third minute? _______________

▪ the sixth minute? _______________

▪ When did the reaction finish? _____

▪ What was the total volume of hydrogen produced? _____________

▪ What was the average rate of the reaction between the time it started and when it finished?

(cm3/min).

____________________________________________________________________________



56) Complete the following table by indicating whether each of the following scenarios would either

increase or decrease the rate of reaction. The first one has been done for you.

Scenario Increase or Decrease

Adding heat Increase

Removing heat

Adding a catalyst

Diluting a solution

Removing an enzyme (catalyst)

Lowering the temperature

Increasing the temperature

Decreasing the surface area

Increasing the concentration of a solution

Breaking a reactant down into smaller pieces

Use the terms to correctly fill in the blanks.

Catalyst energy temperature heat collisions rate of reaction concentration surface area dilute

57) A freshly exposed surface of metallic sodium tarnishes almost instantly if exposed to air and

moisture, while iron will slowly turn to rust under the same conditions. In these two situations, the

__________________ refers to how quickly or slowly reactants turn into products.

58) Adding _________________________ will increase the rate of reaction because this causes the

particles of the reactants to move more quickly, resulting in more collisions and more

______________________.

59) Removing heat will lower the ____________________, causing the particles of the reactants to

slow down, resulting in less frequent collisions.

60) ___________________ refers to how much solute is dissolved in a solution. If there is a greater

concentration of reactant particles present, there is a greater chance that __________________

among them will occur. More collisions mean a higher rate of reaction.

61) A concentrated acid solution will react more quickly than a _______________ acid solution

because there are more molecules present, increasing the chance of collisions.

62) Grains of sugar have a greater ______________________ than a solid cube of sugar of the same

mass, and therefore will dissolve quicker in water.

63) A ______________________, for example an enzyme, is used to speed up a chemical reaction but

is not used up in the reaction itself.



Identify which situation would have a higher reaction rate. Then state the factor that affected the rate

of reaction in each situation.

Situation X Situation Y

Situation with a higher reaction rate

(X or Y)

Factor affecting

the rate of reaction

64)

1 g of sugar (cubes)

1 g of sugar (grains)

65)

5O ºC

O ºC

66)

low number of particles = few collisions

high number of particles = more collisions

67)

enzyme added

no enzyme added



68) Use the following graph to answer the questions

The graph above shows the differences in the rate of reaction at different temperatures,

concentrations, surface area, and the presence or absence of a catalyst. A steeper line represents a

greater rate of reaction. Indicate which line (X or Y) each of the following are associated with.

Which of the four factors affecting reaction rate is most important in each of the following

examples? Choose from concentration, temperature, surface area, and catalyst.

69) Raw carrots are cut into thin slices for cooking.

70) protein is broken down in the stomach by the enzyme pepsin.

71) A woolly mammoth is found, perfectly preserved, near the Arctic.

72) More bubbles appear when a concentrated solution of hydrochloric acid is added to a magnesium

strip than when a dilute solution of the acid is added.

(a) lower temperature ( b) higher temperature

( d) higher concentration (c) lower concentration

(f) presence of a catalyst (e) absence of a catalyst

(g) larger pieces (small surface area)

(h) smaller pieces (large surface area)



Reaction rate laws Rate Law and Specific Rate Constant

Consider a simple chemical reaction in which reactant A is converted into product B according to the

equation below. (one-step reaction)

A→B

Rate law expresses the relationship between the rate of a chemical reaction and the concentration

of reactants.

The rate of reaction is given by the change in concentration of A as a function of time. The expression

for the rate of the reaction can be shown as follows:

rate = k[A]

The specific rate constant (k) is the proportionality constant relating the rate of the reaction to the

concentrations of reactants. As the concentration increase the rate increase.

❖ The rate law and the specific rate constant for any chemical reaction must be determined

experimentally.

❖ The value of the rate constant is temperature dependent.

❖ A large value of the rate constant means that the reaction is relatively fast, while a small value

of the rate constant means that the reaction is relatively slow.

Order of Reaction

In the reaction A→B, the rate of the reaction is directly proportional to the concentration of A raised

to the first power. That is to say, [A]=[A]1.

A first-order reaction is a reaction in which the rate is proportional to the concentration of only one

reactant.

As the concentration of the reactant increase the initial reaction rate increase, on the other hand as

a first-order reaction proceeds, the rate of reaction decreases because the concentration of the

reactants decreases.

The reaction order for a reactant defines how the rate is affected by the concentration of that

reactant.

For example, the rate law for the decomposition of H2O2 is expressed

by the following equation.

Rate = k [H2O2]

73) Why do the decomposition of H2O2 is said to be first order in

H2O2?

Because the reaction rate is directly proportional to the

concentration of H2O2 raised to the first power ([H2O2]1), the

decomposition of H2O2 is said to be first order in H2O2.

If the H2O2 concentration decreases to one-half its original value, the

reaction rate is also reduced by one-half.









Because reaction order is based on reaction rates, it follows that reaction order is also determined

experimentally. Finally, because the rate constant, k, describes the reaction rate, it must also be

determined experimentally.

Other-order reaction rate laws

The rates of some reactions depend on the concentrations of more than one reactant. Consider a

reaction in which a molecule of A collides with a molecule of B to form product C.

aA + bB → C

74) When do a and be equal m and n?

(m = a and n = b) only if the reaction between A and B occurs in a single step (and with a single

activated complex)

75) Does it is common that (m = a and n = b)?

That is unlikely, because single-step reactions are not common.

In order to experimentally determine a rate law, a series of experiments must be performed with

various starting concentrations of reactants. The initial rate law is then measured for each of the

reactions. Consider the reaction between nitrogen monoxide gas and hydrogen gas to form nitrogen

gas and water vapor.

2NO(g)+2H2(g)→N2(g)+2H2O(g)

The rate law for this reaction is

rate=k[NO]2[H2]

▪ the order of the reaction with respect to NO is 2. In other words, rate α [NO]2

▪ the order of the reaction with respect to H2 is 1, or rate α [H2]1

The sum of the exponents is 2+1=3, making the reaction third-order overall.

[A] , [B] : Concentration of reactants A,B m,n : Reaction orders

rate=k[A]m[B]n

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Determining Reaction Order

Method of initial rates

The method of initial rates determines reaction order by comparing the initial rates of a reaction

carried out with varying reactant concentrations.

Consider the general reaction

aA + bB → products.

Suppose that the reaction is carried out three times with varying concentrations of A and B and yields

the initial reaction rates shown in the table,

Experiment Initial [A](M ) Initial [B](M ) Initial Rate (M/s)

1 0.100 0.100 2.00 × 1 0-3

2 0.200 0.100 4.00 × 1 0-3

3 0.200 0.200 16.00 × 1 0-3

Trials 1 and 2 Trials 2 and 3

concentrations

comparison

the concentration of A in Trial 2

is twice that of Trial 1

The concentration of A remains

constant

The concentration of B remains

constant

the concentration of B in Trial 2

is twice that of Trial 1

initial rate

comparison

the initial rate in Trial 2 is twice that

of Trial 1

the initial rate in Trial 3 is (four

times) that

of Trial 2

rates

Because doubling [A] doubles the

rate, the reaction must be

first order in A

2m = 2, m = 1

Because doubling [B] multiplying the

rate four times, the reaction must

be second order in B

2n = 4, n = 2

rate = k[A]m[B]n

rate = k[A]1[B]2

The overall reaction order is third order (sum of exponents 2 + 1 = 3).

76) Write the rate law for the reaction aA → bB if the reaction is third order in A. [B] is not part of the

rate law.

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77) The rate law for the reaction 2NO(g) + O2 (g) → 2NO2(g) is first order in O2 and third order overall.

What is the rate law for the reaction?

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78) Given the experimental data below, use the method of initial rates to determine the rate law for

the reaction aA + bB → products. (Hint: Any number to the zero power equals one. For example,

(0.22) 0 = 1 and (55.6 ) 0 = 1.)

Experiment Initial [A](M ) Initial [B](M ) Initial Rate (M/s)

1 0.100 0.100 2.00 × 1 0-3

2 0.200 0.100 2.00 × 1 0-3

3 0.200 0.200 4.00 × 1 0-3

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Challenge The rate law for the reaction CH3CHO(g) → CH4(g) + CO(g) is Rate = k [CH3CHO]2. Use

this information to fill in the missing experimental data below.

Experiment Initial [CH3CHO] (M) Initial Rate (M/s)

1 2.00 × 1 0-3 2.70 × 1 0-11

2 4.00 × 1 0-3 10.80 × 1 0-11

3 8.00 × 1 0-3

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reaction rates - الرئيسية

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