Lecture 12.1- Interpreting Balanced Equations

Balance the following chemical equations by adding coefficients in front of the compounds.

Example- 2H2 + O2 2H2O

1. MgCl2 + AgNO3 AgCl + Mg(NO3)2

2. C3H8 + O2 CO2 + H2O

3. Al + AgNO3 Ag + Al(NO3)3

4. C12H22O11 C + H2O

An unbalanced equation is mathematically useless!

Bellwork

Balance the following chemical equations by adding coefficients in front of the compounds.

Example- 2H2 + O2 2H2O

1. MgCl2 + AgNO3 AgCl + Mg(NO3)2

2. C3H8 + O2 CO2 + H2O

3. Al + AgNO3 Ag + Al(NO3)3

4. C12H22O11 C + H2O

An unbalanced equation is mathematically useless!

Bellwork

NEVER change subscripts

A balanced chemical equation provides the same kind of quantitative information that a recipe does.

Mass and atoms are conserved in every chemical reaction.

Mass of reactants = mass of products

Number and type of atoms in reactants = number & type atoms in products

A balanced chemical equation can be interpreted in terms of different quantities.

•numbers of atoms

•Molecules

•Moles

•Mass

•volume.

N2(g) + 3H2(g) 2NH3(g)

2 N + 6 H = 2 N + 6HAtoms are conserved!!

N2(g) + 3H2(g) 2NH3(g)

Coefficients tell us the RATIO of molecules

N2(g) + 3H2(g) 2NH3(g)

Coefficients tell us the RATIO of molecules

one N2 + three H2 two NH3

molecule molecules molecules

N2(g) + 3H2(g) 2NH3(g)

Coefficients tell us the RATIO of moles

N2(g) + 3H2(g) 2NH3(g)

one mole + three moles two moles N2 H2

NH3

Coefficients tell us the RATIO of moles

N2(g) + 3H2(g) 2NH3(g)

Find the molar mass of each compound & multiply by the coefficient

N2(g) + 3H2(g) 2NH3(g)

28g + 3 x 2g 2 x 17g

N2(g) + 3H2(g) 2NH3(g)

Find the molar mass of each compound & multiply by the coefficient

28g + 3 x 2g 2 x 17g Why do you multiply the molar mass by three?

N2(g) + 3H2(g) 2NH3(g)

Find the molar mass of each compound & multiply by the coefficient

28g + 3 x 2g 2 x 17g 28g + 6g 34g

N2(g) + 3H2(g) 2NH3(g)

Find the molar mass of each compound & multiply by the coefficient

34g = 34gMass is conserved!

28g + 3 x 2g 2 x 17g 28g + 6g 34g

N2(g) + 3H2(g) 2NH3(g)

Find the molar mass of each compound & multiply by the coefficient

N2(g) + 3H2(g) 2NH3(g) At STP, one mole of gas occupies 22.4 liters.

22.4L N2 + 322.4L H2 222.4L

NH3

N2(g) + 3H2(g) 2NH3(g) At STP, one mole of gas occupies 22.4 liters.

22.4L 22.4L 22.4L 22.4L 22.4L 22.4L

N2(g) + 3H2(g) 2NH3(g) At STP, one mole of gas occupies 22.4 liters.

22.4L N2 + 322.4L H2 222.4L

NH3

22.4L 22.4L 22.4L 22.4L 22.4L 22.4L

N2(g) + 3H2(g) 2NH3(g) At STP, one mole of gas occupies 22.4 liters.

22.4L N2 + 67.2L H2 44.8L

NH3

22.4L N2 + 322.4L H2 222.4L

NH3

Chemists use stoichiometry and mole ratios to calculate how much reactant is needed or how much product will be formed.

The first step in stoichiometry is to get a balanced equation.

The first step in stoichiometry is to get a balanced equation.

H2 + O2 H2O unbalanced (why?)

The first step in stoichiometry is to get a balanced equation.

H2 + O2 H2O unbalanced (why?)

2H2 + O2 2H2O balanced

The first step in stoichiometry is to get a balanced equation.

H2 + O2 H2O unbalanced (why?)

2H2 + O2 2H2O balanced

simple stoichiometry- How many moles of hydrogen gas are needed to make two moles of water?

The first step in stoichiometry is to get a balanced equation.

H2 + O2 H2O unbalanced (why?)

2H2 + O2 2H2O balanced

simple stoichiometry- How many moles of hydrogen gas are needed to make two moles of water?

2 moles of H2(g)

2H2 + O2 2H2O

How many moles of O2 are needed to completely react with 4 moles of H2?

2H2 + O2 2H2O

How many moles of O2 are needed to completely react with 4 moles of H2?

2 moles of O2(g)

Conceptual Problem 12.1

Conceptual Problem 12.1

Conceptual Problem 12.1

Production of iron metal from iron ore–

Fe2O3•H2O(s) + 3CO(g) 2Fe(s) + 3CO2(g) + H2O(g)

In this equation, the volume of gas at STP that reacts and the volume of gas at STP produced will be

a. 3 L and 4 L.

b. 67.2 L and 89.6 L.

c. 67.2 L and 67.2 L

d. 3 L and 3 L

What is conserved in the following reaction?

H2(g) + Cl2(g) 2HCl(g)

a. only mass

b. only mass and number of moles

c. only mass, number of moles, and number of molecules

d. mass, number of moles, number of molecules, and volume