chapter 6perrylocal.org/.../2011/11/6.1_equations_for_chemical_reactions.pdf · general, organic,...

General, Organic, and

Biological Chemistry Fourth Edition

Karen Timberlake

6.1

Equations for

Chemical Reactions

Chapter 6 Chemical Reactions

and Quantities

© 2013 Pearson Education, Inc. Lectures

© 2013 Pearson Education, Inc. Chapter 6, Section 1 2

Chemical Change

A chemical change occurs

when a substance is

converted into one or more

new substances.

Chemical changes can be

recognized by

a change in color,

the formation of a solid, or

the formation of bubbles. A chemical change produces new

substances. When silver (Ag)

reacts with sulfur (S), it produces

silver sulfide (Ag2S).


Evidence of Chemical Change


Learning Check

Identify the visible evidence of a chemical

reaction in each of the following:

1. Methane gas in an outdoor heater burns with

a blue flame.

2. Bleach removes stains from a shirt.

3. Bubbles of CO2 are released when baking

soda is mixed with vinegar.


Solution

Identify the visible evidence of a chemical

reaction in each of the following:

1. Methane gas in an outdoor heater burns with

a blue flame.

heat and a flame

2. Bleach removes stains from a shirt.

color change (color removed)

3. Bubbles of CO2 are released when baking

soda is mixed with vinegar.

formation of gas (bubbles)


Chemical Reactions

A chemical reaction

involves the rearrangement of

atoms.

produces one or more new

substances.

can be observed by the

appearance of new physical

properties. A chemical reaction forms new

products with different properties.

An antacid (NaHCO3) tablet

in water forms bubbles of carbon

dioxide (CO2).


Writing a Chemical Equation

A chemical equation tells us what substances react

(reactants) and what substances are formed

(products).

C(s) + O2(g) CO2(g)

reactants product

(+) used when there is two or more products or reactants

heat is used to start the reaction

(s) the compound is a solid

(l) the compound is a liquid

(g) the compound is a gas

(aq) aqueous, the compound is dissolved in water


Equation for a Chemical Reaction


Balanced Chemical Equations

In a balanced chemical equation, the number of

atoms in the reactants is equal to the number of atoms

in the products for each element.


Balancing Chemical Equations

To balance a chemical equation,

whole number coefficients are placed in front of the chemical formulas.

coefficients in front of a molecule represent the multiple of that molecule needed in a balanced reaction.

subscripts are never changed.


Checking a Balanced Equation

Atoms C 1 1

Atoms H 4 4

Atoms O 4 4

Reactants Products

balanced

balanced

balanced


Guide to Balancing a Chemical

Equation


Steps to Balancing a Chemical

Equation

Balance the following chemical reaction:

Ethanol (C2H6O) burns in the presence of oxygen

gas(O2) to produce steam (H2O) and carbon dioxide

(CO2) gas.

Step 1 Write an equation using the correct formulas

of the reactants and products.



Equation

Step 2 Count the atoms of each element in the

reactants and products.

Reactants Products

not balanced

not balanced

balanced

Atoms of C 2 1

Atoms of H 6 2

Atoms of O 3 3



Equation

Step 3 Use coefficients to balance each element.

Step 4 Check the final equation to confirm it is

balanced.

Create a balance sheet to count atoms of each element.

Reactants Products

balanced

balanced

balanced

Atoms of C 2 2

Atoms of H 6 6

Atoms of O 7 7


Learning Check

Determine if each equation is balanced or not.


Solution


Reactants Products

not balanced

not balanced

Since different numbers of Na and N atoms are present

in the reactants and products, the equation is not

balanced.

Atoms of Na 1 3

Atoms of N 2 1


Solution


Reactants Products

balanced

balanced

balanced

Since the same numbers of C, H and O atoms are

present in the reactants and products, the equation is

balanced.

Atoms of C 2 2

Atoms of H 6 6

Atoms of O 1 1


Write a balanced equation for the reaction of nitrogen gas

(N2) with hydrogen gas (H2) to form ammonia gas (NH3).

Learning Check




Step 1 Write an equation using the correct formulas

of the reactants and products.

Step 2 Count the atoms of each element in the

reactants and products.

Reactants Products

not balanced

not balanced

Solution

Atoms of N 2 1

Atoms of H 2 3






balanced.

Reactants Products

balanced

balanced

Solution

Atoms of N 2 2

Atoms of H 6 6


Check the balance of atoms in the following equation:

1. number of H atoms in products

A. 2 B. 4 C. 8

2. number of O atoms in reactants

A. 2 B. 4 C. 8

3. number of Fe atoms in reactants

A. 1 B. 3 C. 4

Learning Check


Check the balance of atoms in the following equation:

1. number of H atoms in products

C. 8 (4H2O)

2. number of O atoms in reactants

B. 4 (Fe3O4)

3. number of Fe atoms in reactants

B. 3 (Fe3O4)

Solution


Equations with Polyatomic Ions

When balancing equations with polyatomic ions that

remain the same on both sides of the equation,

balance them as a unit.


Balancing with Polyatomic Ions

Balance the following chemical equation. Step 1 Write the equation using the correct formulas of the reactants and products.



Balance the following chemical equation. Step 2 Count the atoms of each element in the reactants and products. Reactants Products

not balanced

not balanced

not balanced

not balanced

Atoms of Na 3 1

PO43− ions 1 2

Atoms of Mg 1 3

Atoms of Cl 2 1





balanced.

Atoms of Na 6 6

PO43− ions 2 2

Atoms of Mg 3 3

Atoms of Cl 6 6

Balance the following chemical equation.

Reactants Products balanced

balanced

balanced

balanced


Balance and list the coefficients from reactants to products.

1. __Fe2O3(s) + __C(s) __Fe(s) + __CO2(g)

A. 2, 3, 2,3 B. 2, 3, 4, 3 C. 1, 1, 2, 3

2. __Al(s) + __FeO(s) __Fe(s) + __Al2O3(s)

A. 2, 3, 3, 1 B. 2, 1, 1, 1 C. 3, 3, 3, 1

3. __Al(s) + __H2SO4(aq) __Al2(SO4)3(aq) + __H2(g)

A. 3, 2, 1, 2 B. 2, 3, 1, 3 C. 2, 3, 2, 3

Learning Check


Balance and list the coefficients from reactants to products.

1. __Fe2O3(s) + __C(s) __Fe(s) + __CO2(g)

B. 2, 3, 4, 3

2. __Al(s) + __FeO(s) __Fe(s) + __Al2O3(s)

A. 2, 3, 3, 1

3. __Al(s) + __H2SO4(aq) __Al2(SO4)3(aq) + __H2(g)

B. 2, 3, 1, 3

2 3 4 3

2 3 3 1

2 3 1 3

Solution

chapter 6perrylocal.org/.../2011/11/6.1_equations_for_chemical_reactions.pdf · general, organic,...

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