CHAPTER 5

Question 1

Which is the First Law of Thermodynamics? Select the one best answer.

The energy of the universe is a constant.

Energy is neither created nor destroyed.

The entropy of the universe either stays the same or increases, but can never decrease.

Both A and B are correct.

Answer 1

Both A and B are correct.

Question 2

Work is?

the amount of gravitational potential energy.

the amount of heat in a body.

the amount of force applied for a particular distance.

none of these.

Answer 2

the amount of force applied for a particular distance.

Question 3

Energy is?

stored work.

the amount of work that can be done.

the capacity to do work.

All of these.

Answer 3

stored work.

Question 4

If W = F.ΔS and F = m.a, we can say that the units for work are?

none of these

kg. m2.s-2
kg. m2.s-1
kg. m.s-2

Answer 4

kg.m2.s-2

Question 5

If KE = 1/2 mv2, we can say that the units for work are:

kg. m.s-2
kg. m2.s-1

none of these

kg.m2.s-2

Answer 5

kg.m2.s-2

Question 6

Given that q=ΔT.c.m, c, the specfic heat, may have units of:

J.g-1K-1 only

J.g.K-1 and J.g.oC-1

J.g-1oC-1 only

J.g-1K-1 and J.g-1oC-1

Answer 6

J.g-1K-1 and J.g-1oC-1

Question 7

Substance A has twice the specific heat of Substance B. When comparing the total heat contained in 1 Kg of substance A and 2 kg of Substance B, when their temperatures are the same, we can say that, under these conditions:

Substance B has twice the amount of thermal energy compared to Substance A.

Substance A has four times the amount of thermal energy compared to Substance B.

Substance A has twice the amount of thermal energy compared to Substance B.

Substance A and Substance B have an equal amount of thermal energy.

Answer 7

Substance A and Substance B have an equal amount of thermal energy.

Question 8

A block of aluminium and a book have been in a room for one week. The room’s temperature has been a constant 25 oC during this time. Someone enters the room and finds that the aluminium block feels colder to touch than the book. The reasons for this are that:

the temperature of the block is lower and heat is transferred faster from the hand to the block than to the book, so the block feels cold.

whilst the temperature of the book and the block are the same, heat is transferred faster from the hand to the block than the book, so it feels cold.

whilst the temperature of the book and the block are the same, heat is transferred faster from the hand to the book than to the block, so the block feels cold.

the temperature of the block is lower and heat is transferred from the hand to the block, whereas the temperature of the book is slightly higher than that of the hand, so the book feels warmer.

Answer 8

whilst the temperature of the book and the block are the same, heat is transferred faster from the hand to the block than the book, so it feels cold.

Question 9

Temperature is best characterized as:

a measure of average thermal energy of a system and comparison of temperatures allows you to determine the direction of heat transfer.

a measure of total thermal energy of a system and comparison of temperatures allows you to determine the direction of heat transfer.

none of these

a measure of total thermal energy of a system only.

Answer 9

a measure of average thermal energy of a system and comparison of temperatures allows you to determine the direction of heat transfer.

Question 10

The first and second laws of thermodynamics could be colloqially described as, respectively:

The best you can do is break even. You can’t break even in every direction

The best you can do is break even. You can break even when you have a very efficient system.

The best you can do is break even. You can’t break even

You can’t break even. The best you can do is break even.

Answer 10

The best you can do is break even. You can’t break even

Question 11

For two bodies, A and B, whose temperatures are indicated respectively as TA and TB, we can say that when the two bodies are at thermal equilibrium:

TA = TB, and their molecules have the same average kinetic energy.

TA≠TB, and their molecules have the same average kinetic energy.

TA=TB, however, for the two bodies, the molecules may have different average kinetic energies.

TA

Answer 11

TA = TB, and their molecules have the same average kinetic energy.

Question 12

Which one of the following statements about units of heat is entirely correct?

A calorie is the amount of energy required to raise one gram of water by 1 °C (or 1 K) and there are 4.2 calories in a joule.

A joule is the amount of energy required to raise one gram of water by 1 °C (or 1 K) and there are 4.2 joules in a calorie.

A joule is the amount of energy required to raise one gram of water by 1 °C (or 1 K) and there are 4.2 calories in a joule.

A calorie is the amount of energy required to raise one gram of water by 1 °C (or 1 K) and there are 4.2 joules in a calorie.

Answer 12

A calorie is the amount of energy required to raise one gram of water by 1 °C (or 1 K) and there are 4.2 joules in a calorie.

Question 13

If the amount of thermal energy in a substance is calculated by q= m.c.T, we can say that the formula used to calculate the amount of heat entering for leaving a substance is:

q= Δm.c.T

q= m.Δc.T

none of these

q= m.c.ΔT

Answer 13

q= m.c.ΔT

Question 14

Specfic heat (heat capacity) is given by the formula:
Which one of the following statements is correct?

ΔT can be calculated using units in either Celsius or Kelvin. Mass is usually expressed in grams.

ΔT can be calculated using units in either Celsius or Kelvin. Mass is usually expressed in kilograms.

ΔT can be calculated using units in Kelvin only. Mass is usually expressed in grams.

ΔT can be calculated using units in Celsius only. Mass is usually expressed in grams.

Answer 14

ΔT can be calculated using units in either Celsius or Kelvin. Mass is usually expressed in grams.

Question 15

In thermodynamics, the Universe is equal to:

none of these

surroundings, ignoring the system.

the system plus its surroundings.

the system that is being studied.

Answer 15

the system plus its surroundings.

Question 16

When q is negative for the system, this means that the system is:

endothermic, and the surroundings gain heat.

endothermic, and the surroundings lose heat.

exothermic, and the surroundings lose heat.

exothermic, and the surroundings gain heat.

Answer 16

exothermic, and the surroundings gain heat.

Question 17

Enthalpy is the heat that is absorbed or evolved from the system under conditions where:

pressure is constant.

no work is done by the system.

volume is constant.

internal energy changes are equal to enthalpy changes.

Answer 17

pressure is constant.

Question 18

For this reaction:
H2(g) + ½ O2(g) ⟶ H2O(l) ΔH = −286kJ
We can say that:

the reaction is exothermic and the amount of heat evolved under constant pressure is 286 kJ/mole of hydrogen gas.

the reaction is endothermic and the amount of heat consumed under constant pressure is 286 kJ/mole of hydrogen gas.

the reaction is exothermic and the amount of heat evolved under constant pressure is 572 kJ/mole of hydrogen gas.

the reaction is endothermic and the amount of heat consumed under constant pressure is 572 kJ/mole of hydrogen gas.

Answer 18

the reaction is exothermic and the amount of heat evolved under constant pressure is 286 kJ/mole of hydrogen gas.

Question 19

For this reaction:
H2(g) + ½ O2(g) ⟶ H2O(l) ΔH = −286kJ
We can say that:

the reaction is exothermic and the reverse reaction is exothermic.

the reaction is exothermic and the reverse reaction is endothermic.

the reaction is endothermic and the reverse reaction is exothermic.

the reaction is endothermic and the reverse reaction is endothermic.

Answer 19

the reaction is exothermic and the reverse reaction is endothermic.

Question 20

The equation for the standard enthalpy of combustion of ethanol is:

C2H5OH(l) ⟶ 2CO2 (g) + 3H2O(l)

C2H5OH(l) + 3O2(g) ⟶ 2CO2 (g) + 3H2O(l)

2C2H5OH(l) + 6O2(g) ⟶ 4CO2 (g) + 6H2O(l)

none of these

Answer 20

C2H5OH(l) + 3O2(g) ⟶ 2CO2 (g) + 3H2O(l)

Question 21

For this equation:
C(s) + O2(g) ⟶ CO2(g) ΔH = −393.5kJ
It would most likely represent the enthalpy of:

combustion of carbon and formation of carbon dioxide.

combustion of carbon only.

formation of carbon dioxide only.

none of these

Answer 21

combustion of carbon and formation of carbon dioxide.

Question 22

Hess’s law states that if a process can be written as the sum of several stepwise processes, the enthalpy change of the total process equals the sum of the enthalpy changes of the various steps.
Hess’s law is valid because:

enthalpy is a state function.

energy is neither created nor destroyed.

ΔU = Δq at constant volume.

entropy is a state function.

Answer 22

enthalpy is a state function.

Question 23

When 2.50 g of methane burns in oxygen, 125 kJ of heat is produced. What is the enthalpy of combustion per mole of methane under these conditions?

802 kJ/mol

-802 kJ/mol

5 kJ/mol

-5 kJ/mol

Answer 23

-802 kJ/mol