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### Unit 5: Stoichiometry

Section 2: Mole:Gram and Gram:Mole

Mole-to-Gram Formula

Use the coefficient from the balanced equation

Use the coefficient from the balanced equation

Mole-to-Gram Problems

Ex-1: How many grams of water are produced at the same time that 100 moles of CO2 are made?

C3H8 + O2 CO2 + H2O

Step 1: Balance the equation

C3H8 + 5O2 3CO2 + 4H2O

Mole-to-Gram Problems

Ex-1: How many grams of water are produced at the same time that 100 moles of CO2 are made?

C3H8 + 5O2 3CO2 + 4H2O

Step 2: Identify the “given” and “unknown” provided in the problem, including the units

G: 100 mol CO2

U: # g H2O

Mole-to-Gram Problems

Ex-1: How many grams of water are produced at the same time that 100 moles of CO2 are made?

C3H8 + 5O2 3CO2 + 4H2O

G: 100 mol CO2 U: # g H2O

Step 3: Begin with the “given” # then choose a conversion factor that has in its denominator the same units as those in the “given”

100 mol CO2 x _______

mol CO2

Mole-to-Gram Problems

Ex-1: How many grams of water are produced at the same time that 100 moles of CO2 are made?

C3H8 + 5O2 3CO2 + 4H2O

G: 100 mol CO2 U: # g H2O

Step 4: The numerator needs to have the same unit as your “unknown.” Use the coefficients in the balanced equation that pertain to its unit to solve.

100 mol CO2 x 4 mol H2O

3 mol CO2

Mole-to-Gram Problems

Ex-1: How many grams of water are produced at the same time that 100 moles of CO2 are made?

C3H8 + 5O2 3CO2 + 4H2O

G: 100 mol CO2 U: # g H2O

Step 5: The 3rd conversion factor allows for the transition from moles H2O to grams H2O through molar mass

100 mol CO2 x 4 mol H2O x 18.02 g H2O = 2402.67

3 mol CO21 mol H2O

Make sure your final answer is in the same # of sig figs that your “given” is in with the correct unit!!!

2000 g H2O or 2x103 g H2O

Mole-to-Gram Practice

Ex-2: How many grams of oxygen are produced at the same time that 0.10 moles of CO2 are made?

C3H8 + 5O2 3CO2 + 4H2O

5.3 g O2

Mole-to-Gram Practice

Ex-3: How many grams of C3H8 are produced at the same time that 35.0 moles of O2 are made? C3H8 + O2 CO2 + H2O

C3H8 + 5O2 3CO2 + 4H2O

G: 35.0 mol O2 U: # g C3H8

35.0 mol O2 x 1 mol C3H8 x 44.11 g C3H8 = 308.77

5 mol O21 mol C3H8

309 g C3H8

Gram-to-Mole Formula

Use the coefficient from the balanced equation

Use the coefficient from the balanced equation

Gram-to-Mole Problems

Ex-1: How many moles of NO are produced at the same time as 100 grams of H2?

NH3 + O2 NO + H2

Step 1: Balance the equation

2NH3 + O2 2NO + 3H2

Gram-to-Mole Problems

Ex-1: How many moles of NO are produced at the same time as 100 grams of H2?

2NH3 + O2 2NO + 3H2

Step 2: Identify the “given” and “unknown” provided in the problem, including the units

G: 100 g H2

U: # mol NO

Gram-to-Mole Problems

Ex-1: How many moles of NO are produced at the same time as 100 grams of H2?

2NH3 + O2 2NO + 3H2

G: 100 g H2 U: # mol NO

Step 3: Begin with the “given” # then choose a conversion factor that has in its denominator the same units as those in the “given”… this is its molar mass. The numerator will always be 1 mole of the “given” units

100 g H2 x 1 mol H2

2.02 g H2

Gram-to-Mole Problems

Ex-1: How many moles of NO are produced at the same time as 100 grams of H2?

2NH3 + O2 2NO + 3H2

G: 100 g H2 U: # mol NO

Step 4: The 3rd conversion factor has moles of the “given” in its denominator and the moles of the “unknown” in its numerator. Take the numbers from the coefficients from the balanced equation.

100 g H2 x 1 mol H2 x 2 mol NO = 33.003

2.02 g H2 3 mol H2

Make sure your final answer is in the same # of sig figs that your “given” is in with the correct unit!!!

30 mol NO

Gram-to-Mole Practice

Ex-2: How many moles of NH3 are produced at the same time as 25 grams of O2?

NH3 + O2 NO + H2

2NH3 + O2 2NO + 3H2

G: 25 g O2 U: # mol NH3

25 g O2 x 1 mol O2 x 2 mol NO = 1.5625

32.00g O2 1 mol O2

1.6 mol NH3

Gram-to-Mole Practice

Ex-3: How many moles of NO are produced at the same time as 670 grams of NH3?

NH3 + O2 NO + H2

2NH3 + O2 2NO + 3H2

G: 670 g NH3 U: # mol NO

670 g NH3 x 1 mol NH3 x 2 mol NO = 39.319

17.04g NH3 2 mol NH3

39 mol NO

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