Chemical Reactions

Theme: Changes and Reactions

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color melting point boiling point electrical conductivity specific heat density state (solid, liquid, or gas)

Physical Properties (Review)

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Changes in physical properties melting boiling condensation

No change occurs in the identity of the substance

Example:

Ice , rain, and steam are all water

Physical Change (Review)

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Atoms in the reactants are rearranged to form one or more different substances

Old bonds are broken; new bonds form

Examples:

Fe and O2 form rust (Fe2O3)

Ag and S form tarnish (Ag2S)

Chemical Change

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Classify each of the following as a

1) physical change or 2) chemical change

A. ____ a burning candle

B. ____ melting ice

C. ____ toasting a marshmallow

D. ____ cutting a pizza

E. ____ polishing silver

Learning Check 1

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Classify each of the following as a

1) physical change or 2) chemical change

A. __2__ a burning candle

B. __1_ melting ice

C. __2__ toasting a marshmallow

D. __1__ cutting a pizza

E. __2__ polishing silver

Solution 1

Main Ideas

Chemical Reactions are represented by Chemical Equations.

Main Ideas

Chemical Equations are balanced to show the same number of atoms of each element on each side.

The Law of Conservation of Matter (Mass) says that atoms won’t be created or destroyed in a chemical reaction. That is why chemical equations must be balanced!

Chemical Reactions are Everywhere

Cooking Respiration

Chemical Reactions are Everywhere

Hair Dye Auto Fuel

Vocab

Reactants Products Chemical Formula Chemical Equation Coefficients

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A process in which at least one new substance is produced as a result of chemical change.

Chemical Reaction

Chemical Equations

Reactants produce Products Reactants Products

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Reactants Products

A Chemical Reaction

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A. How does an equation indicate a change in

the identity of the reacting substances?

B. How did the yellow and green reactants

combine?

C. Did all the reactants form product? Why or

why not?

Learning Check 2

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A. How does an equation indicate a change in the identity of the reacting substances? The formulas of the reactants are different than the formulas of the products.

B. How did the yellow and green reactants combine? 1 yellow combined with 1

green.C. Did all the reactants form product? Why or why not? No. There were more yellow reactants than green.

Solution 2

How do you know when a chemical reaction takes place?

Color Change Precipitate Formation

Gas Formation Odor

Temperature Change Change in Acidity

Representing Chemical Reactions

Chemists observe chemical reactions and have come up with a way to represent or model what is happening.

Making NaCl Solid Sodium combines with Chlorine

gas to make solid Sodium Chloride:

2Na (s) + Cl2 (g) 2NaCl

Chemical Equations are different from Numerical Equations

Numerical Equation: 3x + 2y = 47 Chemical Equation 2Na + Cl2 2NaCl Reactant A + Reactant B Product The reactants are used up in forming

the product The arrow shows the direction of the

reaction

Components of a Chemical Equation

2H2 + O2 2H2O

(Reactants)

(Products)(Yield)

Chemical Formulas

Chemical Formula

Subscripts CoefficientCoefficient Subscript

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Chemical symbols give a “before-and-after” picture of a chemical reaction

Reactants Products

MgO + C CO + Mg

magnesium oxide to produce carbon monoxide

reacts with carbon and magnesium

Writing a Chemical Equation

Law of Conservation of Matter (Mass)

Matter cannot be created or destroyed. However, it can change form.

The mass of the reactants must equal the mass of the products in a chemical reaction.

Balancing Chemical Equations

In other words, The total number of each type of

atom must be the same on both sides of the equation.

Understanding Chemical Formulas

Subscripts BaF2 the 2 in this formula is

called the subscript. It refers only to the element preceding it. In this case the F (fluorine).

Understanding Chemical Formulas

Parentheses Al(NO3)3

in some chemical

formulas it is necessary to use parentheses. The subscript outside the parentheses refers to all the elements inside the parentheses. In this example there are: one Al (aluminum), three N

(nitrogen), and nine O (oxygen).

Understanding Chemical Formulas

Coefficients 3 BaF2 the 3 in this formula is

called the coefficient. It refers to each element that follows. In this case there would be 3 Ba (barium) and 3 F2

(a total of 6 fluorine).

Reaction Rates

Increasing Temperature increases reaction rate

Surface Area – increasing the surface area increases the rate of reaction.

Concentration – amount of reactants in a given volume.

Stirring increases reaction rate

Reaction Rates - Catalysts

Catalyst – speeds up a reaction but does not change during the reaction

Catalysts do not get used up in a reaction

HCl CH3COCH3 + I2 CH3COCH2I

+ HI

HCl is a catalyst, necessary for the reaction but not used up in the reaction, that is why it is written above the reaction arrow.

Reaction Rates

Increasing reactants increases the rate of reaction and increases the products made

Reactions will occur until at least one of the reactants is all used up

Mass of all the reactants is equal to the mass of all the products

Reaction Rates - Spectrophotometer

Spectrophotometer measures absorbance or transmission of light

Can be used to measure the disappearance or appearance of products or reactants in a chemical reaction