CHM 2045C Module Six Sample Exam Answers
Part F Volume-Volume Stoichiometry 5 points
In the Haber process, nitrogen N2 and hydrogen H2 gases combine to give ammonia gas NH3 as the only product. If 5.55 L of nitrogen gas completely reacts, calculate the volume of ammonia that is produced. Assume all volumes of gas are measured under constant conditions of 500 oC and 300 atm pressure. How many liters of hydrogen are required to complete react the 5.55L of nitrogen?
Using ChemiCalc to balance the equation.
Step #1 Write the balanced reaction
N2 + 3 H2 à 2 NH3
Step #2 Write the question in Dimensional Analysis format:
__?__ L N2 = 5.55 L NH3
Step #3 Setup the dimensional analysis problem.
Think about the Road map of Stoichiometry:
It is one step with a direct volume to volume unit factor similar to the mole ratio. See (f) above.
See Section 10.6 of Chapter 10 as this is the very problem from your textbook on page 264.
First answer is 11.1 L NH3
Second Question: __?__ L H2 = 5.55 L NH3
Second answer: 16.65 L H2
Part G Mass-Volume Stoichiometry 5 points
Potassium chlorate is used in the lab to make oxygen gas by the following (unbalanced) reaction:
KClO3 à KCl + O2
How liters of oxygen at STP may be made from reacting 1.226 grams of Potassium chlorate?
Step #1: Write and Balance the Equation:
2 KClO3 à 2 KCl + 3 O2
Step#2 Write the question in Dimensional Analysis format:
__?__ L O2 = 1.226 g KClO3
Step#3 Think about the Stoichiometry Road Map
a. Change grams of KCLO3 to moles KCLO3 using molar mass of KCLO3
b. Change moles of KCLO3 to moles O2 using the mole ratio from the balanced equation.
c. Change moles of O2 to Liters of O2 using the molar gas volume constant assuming STP.
Step #4 Setup and Solve the Dimensional Analysis Sequence:
Your answer is 0.336 L O2