Thermochemistry Test Review

SCH4U Thermochemistry Test Review

Try all the problems previously assigned, look at the problems in your textbook, and try these:
1. Be sure to understand the following vocabulary:
Thermochemistry
Thermochemical Equation
System
Surrounding
Calorimetry
calorimeter
Heat
temperature thermal energy chemical energy
Open, closed, isolated/insulated systems enthalpy change
Molar enthalpy
Exothermic changes
Endothermic changes
Hess’s Law
Heat capacity specific heat capacity combustion standard heat of formation standard molar enthalpy of reaction (∆Hcomb, ∆Hvap, ∆Hsol etc.)
Heat flow diagram
Potential Energy Diagram 2. The standard molar heat of combustion for benzene C6H6(l) is -6542 kJ/mol.

a) Write a thermo chemical equation for the reaction.
b) What is the enthalpy change per mole of CO2 (kJ/mol of CO2)
c) Calculate the amount of heat energy released by the combustion of 100.0 g of benzene.
d) Draw an enthalpy diagram for the reaction
e) What mass of benzene must be combusted to heat a water tank of 5.00 L of water from 10.0 oC to 60.0 0C.

3. Communicate the enthalpy change by using the four methods described in this section
(a) The formation of acetylene (ethyne, C2H2) fuel from solid carbon and gaseous hydrogen (H° = +228 kJ/mol acetylene)
b) the exothermic combustion of C2H5OH (H° =–3.47 MJ/mol of alcohol)

4. A 235g stick of a metal at 100.0oC is thrust into 245 g of cold water (of temperature 10.0oC). If the final temperature observed for the whole system is 15.0oC, calculate the specific heat capacity of the given metal.

5. Exactly 4.86 grams of an unknown organic compound is burned in a constant volume calorimeter, containing 6.80 kg of water. The calorimeter has a heat capacity of 512 J Co -1. The temperature changes from 20.00o C to 20.86o C. Assuming the formula weight of the compound is 386.8 grams per mol, calculate the molar heat of reaction ΔHc of this compound.

6. As an alternative to combustion of coal gas described earlier in this section, coal gas can undergo a process called methanation.
3 H2(g) + CO(g) --------> CH4(g) + H2O(g) ∆H =?

Determine the enthalpy change involved in the reaction of 300 g of carbon monoxide in this methanation reaction, using the following reference equations and enthalpy changes.
(1) 2 H2(g) + O2(g) --------> 2 H2O(g) ∆H1 = -483.6 kJ
(2) 2 C(s) + O2(g) -------->. 2 CO(g) ∆H2 = -221.0 kJ
(3) CH4(g) + 2 O2(g) --------> CO2(g) + 2 H2O(g) ∆H3 = -802.7 kJ
(4) C(s) + O2(g) --------> CO2(g) ∆H4 = -393.5 kJ

8. a) Calculate Ho for the following reaction.

b. State whether the reaction is exothermic or endothermic.
c. Rewrite the equation as a thermochemical equation to include the heat term.
d. Indicate whether the products have a greater or smaller enthalpy than the reactants.

9. Use the standard enthalpies of formation to determine the change in enthalpy for the following reactions
CH4 (g) + 2 O2 (g) ---------> CO2 (g) + 2 H2O (l) ∆Hf of CH4 = --74.4 kJ /mol
10. If the heat of formation of sodium chlorate is –53 kJ/mol, then the heat of reaction for 3 mol of sodium chlorate is ;

11. If 335 g of water at 24.5ºC absorbed 2.66 kJ of energy, what is the final temperature of the water?

12. Many cigarette lighters contain liquid butane. C4H10 (l). Using Enthalpies of formation calculate the quantity of heat produced when 1.0 g of butane is completely burned in air. (∆H˚f – Butane(l) = –147.6kJ/mol) ?

12. Do you think it is wise to make a calorimeter out of a material with a low or high heat capacity? Why?

13. What assumptions do we make when using doing calorimetry? When might we discard these assumptions?

14. Thermal equilibrium defines the point where all parts of a system (or system and surroundings) are at the same temperature. It does not define the point at which all parts of the system have the same amount of thermal energy. Why is this?

15. An object can possess thermal energy but cannot possess heat. Explain why, highlighting the difference between the two terms.

16. One way to heat water in a home or cottage is to burn propane. If 4.50 g of propane burns, what temperature change will be observed if all of the heat from combustion transfers into 4.0 kg of water?

17. Naphthalene (C10H8) is a solid aromatic compound often sold as moth balls. The molar heat of combustion of Naphthalene is -5154 kJ.
a) Write a balanced equation for the formation of Naphthalene
b) Calculate the standard enthalpy of formation of Naphthalene from the given information.