Chemical CalculationsChemical Calculations

Prentice-Hall Chapter 12.2Prentice-Hall Chapter 12.2Dr. YagerDr. Yager

ObjectivesObjectives

ConstructConstruct mole ratios from balanced mole ratios from balanced chemical equations and chemical equations and applyapply these ratios these ratios in stoichiometric calculations.in stoichiometric calculations.

CalculateCalculate stoichiometric quantities from stoichiometric quantities from balanced chemical equations using units of balanced chemical equations using units of moles, mass, representative particles and moles, mass, representative particles and volume of gases at STP.volume of gases at STP.

A A mole ratiomole ratio is a conversion factor derived from is a conversion factor derived from the coefficients of a balanced chemical equation the coefficients of a balanced chemical equation and interpreted in terms of moles.and interpreted in terms of moles.

In chemical calculations, In chemical calculations, mole ratiosmole ratios are used to are used to convert between moles of reactant and moles of convert between moles of reactant and moles of product, between moles of reactants, or between product, between moles of reactants, or between moles of products.moles of products.

Mole RatiosMole Ratios

NN22(g)(g) + 3H + 3H22(g) (g) 2NH 2NH33(g)(g)

1 mole of nitrogen reacts with 3 moles of hydrogen1 mole of nitrogen reacts with 3 moles of hydrogen

Mole ratios are used to convert between any two Mole ratios are used to convert between any two compounds:compounds:

3

2

2

3

2

2

NH moles 2

H moles 3 ,

N mole 1

NH moles 2 ,

H moles 3

N mole 1

Mole-Mole CalculationMole-Mole Calculation

If you have 0.60 mol of NIf you have 0.60 mol of N22, how much NH, how much NH33 is is

produced?produced?

The ratios are:The ratios are:

3

2

2

3

2

2

NH moles 2

H moles 3 ,

N mole 1

NH moles 2 ,

H moles 3

N mole 1

3

2

32 NH mol 1.2

N mol 1NH mol 2

x N mol 0.60

Write the six mole ratios for:Write the six mole ratios for:

4Al4Al(s)(s) + 3O + 3O22(g)(g) 2Al 2Al22OO33(s)(s)

Write the six mole ratios for:Write the six mole ratios for:

4Al4Al(s)(s) + 3O + 3O22(g)(g) 2Al 2Al22OO33(s)(s)

O mol 3

Al mol 2 ,

Al mol 2O mol 3

,Al mol 4

Al mol 2

Al mol 2

Al mol 4

Al mol 4O mol 3

O mol 3Al mol 4

2

2

2

22

2

2

2

3

3

3

3

O

O

O

,O

,,

How many moles of aluminum are needed to How many moles of aluminum are needed to form 3.7 mol of Alform 3.7 mol of Al22OO33??

How many moles of aluminum are needed to How many moles of aluminum are needed to form 3.7 mol of Alform 3.7 mol of Al22OO33??

Al mol 7.4 Al mol 2

Al mol 4x Al mol3.7

2

2 3

3 OO

Mass-Mass CalculationMass-Mass Calculation

Calculate the number of grams formed by Calculate the number of grams formed by reacting 5.4 grams of Hreacting 5.4 grams of H22 with excess N with excess N22..

NN22(g)(g) + 3H + 3H22(g) (g) 2NH 2NH33(g)(g)

NN22(g)(g) + 3H + 3H22(g) (g) 2NH 2NH33(g)(g)

Calculate the number of grams formed by Calculate the number of grams formed by reacting 5.4 grams of Hreacting 5.4 grams of H22 with excess N with excess N22..

3

3

3

2

3

2

22 NH g 31

NH mol 1NH g17

xH mol 3

NH mol 2x

H g 2.0H mol 1

x H g 5.4

Other Stoichiometric CalculationsOther Stoichiometric Calculations It all comes down to moles.It all comes down to moles.

If you want atoms, particles, etc. then multiply If you want atoms, particles, etc. then multiply moles by 6.02x10moles by 6.02x102323

If you want gas volume at STP then multiply If you want gas volume at STP then multiply moles by 22.4 liters.moles by 22.4 liters.

If you have volume divide by 22.4 L/mol to get If you have volume divide by 22.4 L/mol to get molesmoles

Always use dimensional analysis to check Always use dimensional analysis to check units! units!

Solution DiagramSolution Diagram

12.2

Problem-Solving ApproachProblem-Solving Approach

12.2

1. How many moles of water are produced 1. How many moles of water are produced when 2.5 mol of Owhen 2.5 mol of O22 react according to the react according to the

following equation?following equation?

CC33HH88 + 5O + 5O22 3CO 3CO22 + 4H + 4H22O O

a)a) 2.02.0

b)b) 2.52.5

c)c) 3.03.0

d)d) 4.04.0

1. How many moles of water are produced 1. How many moles of water are produced when 2.5 mol of Owhen 2.5 mol of O22 react according to the react according to the

following equation?following equation?

CC33HH88 + 5O + 5O22 3CO 3CO22 + 4H + 4H22O O

a)a) 2.02.0

b)b) 2.52.5

c)c) 3.03.0

d)d) 4.04.0

2. Nitrogen gas reacts with hydrogen gas to 2. Nitrogen gas reacts with hydrogen gas to

produce ammonia gas. produce ammonia gas.

NN22((gg) + 3H) + 3H22((gg) ) 2NH 2NH33((gg) )

What volume of HWhat volume of H22 is required to react with 3.00 L of N is required to react with 3.00 L of N22, and , and

what volume of NHwhat volume of NH33 is produced at 0°C? is produced at 0°C?

a)a) volume of Hvolume of H2 2 = 9.00 L, volume of NH= 9.00 L, volume of NH33 = 6.00 L = 6.00 L

b)b) volume of Hvolume of H22 = 3.00 L, volume of NH = 3.00 L, volume of NH33 = 3.00 L = 3.00 L

c)c) volume of Hvolume of H22 = 3.00 L, volume of NH = 3.00 L, volume of NH33 = 6.00 L = 6.00 L

d)d) volume of Hvolume of H22 = 1.00 L, volume of NH = 1.00 L, volume of NH33 = 1.50 L = 1.50 L

2. Nitrogen gas reacts with hydrogen gas to 2. Nitrogen gas reacts with hydrogen gas to

produce ammonia gas. produce ammonia gas.

NN22((gg) + 3H) + 3H22((gg) ) 2NH 2NH33((gg) )

What volume of HWhat volume of H22 is required to react with 3.00 L of N is required to react with 3.00 L of N22, and , and

what volume of NHwhat volume of NH33 is produced at 0°C? is produced at 0°C?

a)a) volume of Hvolume of H2 2 = 9.00 L, volume of NH= 9.00 L, volume of NH33 = 6.00 L = 6.00 L

b)b) volume of Hvolume of H22 = 3.00 L, volume of NH = 3.00 L, volume of NH33 = 3.00 L = 3.00 L

c)c) volume of Hvolume of H22 = 3.00 L, volume of NH = 3.00 L, volume of NH33 = 6.00 L = 6.00 L

d)d) volume of Hvolume of H22 = 1.00 L, volume of NH = 1.00 L, volume of NH33 = 1.50 L = 1.50 L

3. 3. Automotive airbags inflate when sodium azide, Automotive airbags inflate when sodium azide, NaNNaN33, rapidly decomposes to its component , rapidly decomposes to its component

elements via this reaction: elements via this reaction:

2NaN2NaN33 2Na + 3N 2Na + 3N22. .

How many grams of sodium azide are required How many grams of sodium azide are required to form 5.00 g of nitrogen gas?to form 5.00 g of nitrogen gas?

a)a) 11.61 g11.61 g

b)b) 17.41 g17.41 g

c)c) 7.74 g7.74 g

d)d) 1.36 g1.36 g

3. 3. Automotive airbags inflate when sodium azide, Automotive airbags inflate when sodium azide, NaNNaN33, rapidly decomposes to its component , rapidly decomposes to its component

elements via this reaction: elements via this reaction:

2NaN2NaN33 2Na + 3N 2Na + 3N22. .

How many grams of sodium azide are required How many grams of sodium azide are required to form 5.00 g of nitrogen gas?to form 5.00 g of nitrogen gas?

a)a) 11.61 g11.61 g

b)b) 17.41 g17.41 g

c)c) 7.74 g7.74 g

d)d) 1.36 g1.36 g