## Chem – Stoichiometry Conversion Ratios

STOICHIOMETRY CONVERSION RATIOS (MOLE TO MOLE RATIOS):

Many students think stoichiometry is a scary and evil word, but it is just another type of conversion we see in chemistry. Stoichiometry is using the coefficients of a chemical equation to set up a conversion with them. Lets look at an example of what I am talking about with the chemical equation below. Ignore the states of the equation. They are not important in stoichiometry.

N2(g) + 3 H2(g) —-> 2 NH3(g)

From this chemical equation we can state some of the stoichiometry ratios:

What is the ratio between the N2 and the H2?

 1 N2 3 H2

or

 3 H2 1 N2

What is the ratio between the N2 and the NH3?

 1 N2 2 NH3

or

 2 NH3 1 N2

What is the ratio between the H2 and the NH3?

 3 H2 2 NH3

or

 2 NH3 3 H2

VIDEO Stoichiometry Ratios Demonstrated Example 1: For the chemical equation below what is the ratio of oxygen to H2?

H2SO4(aq) —> H2(g) + S(s) + 2 O2(g)

How do we set up the ratio?

Answer: O2 on top and H2 on bottom

 O2 H2

What numbers do we put in front of each?

Answer: The coefficients of each in the chemical equation

 2 O2 1 H2

VIDEO Stoichiometry Ratios Demonstrated Example 2: For the chemical equation below what is the ratio of H2O to O2?

2 C5H7OH(l) + 13 O2(g) ——> 10 CO2(g) + 8 H2O(g)

How do we set up the ratio?

Answer: H2O on top and O2 on bottom

 H2O O2

What numbers do we put in front of each?

Answer: The coefficients of each in the chemical equation

 8 H2O 13 O2

PRACTICE PROBLEMS: Give the stoichiometry (coefficient) ratio for the questions below.

What is the ratio of Fe2O3 to FeP?

4 P + 2 Fe2O3 ——> 4 FeP + 3 O2

 2 Fe2O3 4 FeP

What is the ratio of Al2S3 to PbS2?

3 PbS2 + 4 AlPO4 ——> 2 Al2S3 + Pb3(PO4)4

 2 Al2S3 3 PbS2

What is the ratio of MgO to KF?

MgO + 2 KF ——> MgF2 + K2O

 1 MgO 2 KF

What is the ratio of LiNO3 to Ba?

2 Li + Ba(NO3)2 ——> Ba + 2 LiNO3

 2 LiNO3 1 Ba  