AP Chemistry                                                               Unit 6

Chapter 6                                                                     Thermochemistry        

Test 6

Directions:The test is divided into 2 parts multiple guess and free response. Answer any 10 multiple guess (3 points each) and any 2 free response (15 pts each). It is suggested you do the free response first. Answer on the provided answer blank at the appropriate location. Remember: ”Be both a speaker of words and a doer of deeds” Homer 700BC

 

Multiple Guess

Nature of energy

1. The First Law of Thermochemistry says

  1. Energy is the ability to do work
  2. Work is force times distance
  3. Kinetic energy is energy of motion
  4. The total amount of energy in the universe is a constant
  5. none of these

 

2. When addressing the issue of system and surroundings remember system refers to

     a. system is chemicals reacting, surroundings are the environment

     b. surroundings are chemicals reacting, system is the environment

     c. system refers to reactants, surroundings refers to products

    d. surrounding refers to reactants, system refers to products

    e. none of these

 

3. Calculate energy change for a system if 20 joules are removed from a system and 15 joules of work are done by the system

  1. ΔE is –5 joules
  2. ΔE is –35 joules
  3. ΔE is +5 joules
  4. ΔE is +35 joules
  5. None of these

 

4. A balloon is reduced in volume from 4,500,000 L to 4,000,000 L  by the surroundings. A removal of 13,000,000 J of energy from the system also occurs . Assuming this takes place under normal atmospheric conditions of 1 atm, determine energy change for the system

  1. 0.09 Liter atm
  2. 0.57 Joules
  3. 1.11 Kilojoules
  4. 4.92 Liter atm
  5. none of these

 

 

Enthalpy and Calorimetry

5. Enthalpy is a defined state function of a chemical system. Its most easily described meaning is for a constant pressure system the change in enthalpy is

     a. ΔV (change in volume for the system)

     b. ΔT (change in temperature of a system)

     c. heat flow (change in energy of a system) of a system

    d. C (heat capacity of a system)

     e. none of these

 

6. Determine the heat capacity of a calorimeter if 100g of water at 100˚C is added to a 25g calorimeter at 20˚C and their equilibrium temperature is 95˚C

  1. 233.5 j/g˚C
  2. 13.8 j/g˚C
  3. 1.1 J/g˚C
  4. 0.051 J/g˚C
  5. none of these

 

 

Hess’s Law

7. Hess’s Law states the change in enthalpy of a system

  1. is the sum of the individual enthalpy changes of a reaction
  2. is the mass times heat capacity times difference in temperature for a system
  3. is the product of pressure times change in volume
  4. is the quotient of product energy divided by (mass times grams of sample)
  5. none of these

 

8. Select the true statement for solution of Hess’s Law

     a. if a reaction is reversed, reverse the sign of ΔH

     b. the magnitude of ΔH is proportional to the quantities in the reaction

     c. both of these are true

     d. neither of the above are true

 

9. What is the energy change for the following system (use appendix 22)

                        2N2O(g) + O2(g) à 4NO(g)

     a. +526 kj

     b. +347 kj

     c. +196 kj

     d. -122 kj

     e. none of these

 

Standard Enthalpies

10. Standard enthalpy of Formation is defined as

  1. amount of energy needed to form a mole of product using molecules
  2. amount of energy needed to form a mole of product using atoms
  3. amount of energy needed to use up a mole of reactant molecules
  4. amount of energy needed to use up a mole of reactant atoms
  5. none of these

 

11. Select the FALSE statement about enthalpy calculations

     a. the enthalpy of an element in standard state is 0

     b. when a reaction is reversed the magnitude of ΔH remains the same

     c. when a reaction is reversed the sign of ΔH is opposite

     d. the enthalpy of a reaction is the sum of the enthalpies for each part of the reaction

     e. all of these are true

 

Present Sources of Energy

12. Select the source of energy NOT a major component (less than 1%) in today’s society

a wood

b coal

c petrochemicals

d nuclear/hydro

e none of these

 

 

13. Analysis of reserves places which source of energy in greatest concern.

a.       wood

b.       coal

c.       petrochemicals

d.       nuclear/hydro

e.       None of these are of immediate concern

 

 

14. Climate change concerns revolve around a phenomenon called greenhouse effect, which is

a.       Depletion of O2 makes the atmosphere unusable for humans

b.       Conversion of N2 makes for overabundance of natural fertilizers in the soil

c.       Increases in CO2 make the average global temperature increase

d.       Decreases in oxygen and ozone (O3) allow harmful UV to contact earth

e.       none of these

 

 

New Energy Sources

15. Proposals for new energy sources do NOT include

a.       coal conversion

b.       hydrogen

c.       alcohols

d.       oil shale

e.       All of these are possibilities

 

 

Free Response

 

16. 100 ml of water at 100˚C is added to a 37.0 g calorimeter at 20˚C. The resulting equilibrium temperature of the system is 96˚C. What is the heat capacity of the calorimeter? Assume the density of water is 1 g/ml.

 

 

17. A balloon with 45 moles of Helium has a volume of 890 liters at 0˚C and 1 atm. The temperature of the Helium system is increased to 40˚C as it expands to 950 liters (pressure constant, heat capacity of helium is 20.8 J/g˚C). Find

     a. q for the gas

     b. w for the system

     c. ΔE for the system

 

 

18. Find the additive enthalpy change for the following reaction

 

            C2H2 (g) + 5/2 O2 (g) à 2CO2 (g)  +  H2O(l)

Given

2C + H2 à C2H2(g)                     ΔH =  227 kJ/mole

C + O2 à CO2(g)                         ΔH = -393.5 kj/mole

H2 + ½ O2 à H2O(l)                   ΔH = -286 kj/mole