Stoichiometry meets Thermochemistry Worksheet
1. In your words, describe how you would recognize an exothermic and an endothermic reaction if you felt one or you were looking at one written on paper.
2. ___CH4 (g) + ___O2 (g) ___H2O (g) + ___CO2 (g) + 212.8 kcal
Balance the above equation showing the combustion of methane (CH4) and answer these questions:
a. Is this reaction exothermic or endothermic?
b. How many moles of methane (CH4) are needed to make 5.98 x 105 kcal of heat?
c. If 445.2 kcal are released in this reaction, how many moles of oxygen were used? grams of oxygen?
d. If a reaction produced 3.88 x 104 g of CO2, how much heat did it produce?
A NEW LESSON: Every endothermic reaction is an exothermic reaction in reverse and every exothermic reaction is an endothermic reaction in reverse! Yes, you can switch around the entire equation above so that the 212.8 kcal of heat is now a reactant that informs us of the amount of heat needed to make methane (CH4). It would then look like this:
___H2O (g) + ___CO2 (g) + 212.8 kcal ___CH4 (g) + ___O2 (g)
e. How much heat is needed to produce 10.5 moles of methane gas?
f. How much heat is needed to produce 4.5 x 103 grams of methane gas?
g. Which reaction makes more heat: the combustion of methane or the synthesis of water? (See the notes “On Heat and other Matter” for the synthesis of water. The combustion of methane is on the front of this worksheet). Explain your response.
3. The overall reaction in the combustion of iron can be present as:
___Fe (s) + ___O2 (g) ___Fe2O3 (s) + 1652 kJ
a. Is the reaction an endothermic or exothermic reaction?
b. Rewrite the reaction as the opposite reaction for what you answered in (a.) and put the heat in the appropriate place in the reaction.
c. How much heat is released when 4.50 moles of iron is reacted with excess oxygen?
d. How much heat is released when 8.00 moles of iron (III) oxide is formed?
e. How much heat is needed to produce 5.00 moles of solid iron?
f. How much heat is released when 10.0 g of Fe and 2.00 g of O2 are reached?
4. One Chunk: On your own sheet of paper and in your own words, explain the familiar process of ice melting in a glass of water. Is the reaction endothermic or exothermic? Identify the system and the surroundings. Explain the reaction completely using the kinetic molecular theory.