multiple choice

Question 1

Answer 1

D

Question 2

Answer 2

MolarenthalpyforH₂= −91.8kJ / 3 =−30.6 kJ/mol

Question 3

In Equation II (from the previous question), methane
CH₄(g) is formed from solid carbon and hydrogen gas. The enthalpy change ΔH° for this reaction is negative

Answer 3

In Equation II (from the previous question), methane
CH₄(g) is formed from solid carbon and hydrogen gas. The enthalpy change ΔH° for this reaction is negative, meaning that energy is released, and methane contains less chemical potential energy than the reactants.

Methane is a fossil fuel, and the chemical potential energy in fossil fuels originally comes from the energy stored by ancient biological matter, which ultimately comes from the Sun through photosynthesis.

Thus, the correct row is: Row A: less and the Sun.

Question 4

Answer 4

C

Question 5

Answer 5

D

Question 6

Answer 6

2542

Question 7

Answer 7

4123

Question 8

Answer 8

B

Question 9

Answer 9

D

Question 10

Answer 10

19.9

Question 11

Answer 11

D

Question 12

Answer 12

A

Question 13

Answer 13

C

Question 14

Answer 14

A.
Here’s why:
During the combustion of propane, the primary energy change involves potential energy because it comes from the breaking and forming of chemical bonds. This is a rearrangement of bonds as the propane reacts with oxygen to form carbon dioxide and water, releasing energy in the process.
Kinetic energy and molecular motion aren’t the main factors involved in the energy release mechanism itself but are secondary effects of the combustion process. Hence, “potential energy resulting from a rearrangement of bonds” is the correct answer.

Question 15

Answer 15

C

Question 16

Answer 16

A

Question 17

Answer 17

A

Question 18

Answer 18

C
The question is asking for an interpretation of the data provided in the table that shows the molar enthalpy of combustion for different fuels, with an increasing number of carbon atoms in the molecules (from methane to octane). The molar enthalpy values become more negative as the number of carbon atoms increases.

This means more energy is released during combustion as the number of carbon atoms increases, which leads to the correct answer being:

c. greater the energy released during combustion

This interpretation aligns with the fact that larger fossil fuel molecules release more energy when burned due to their higher number of chemical bonds that break and form during combustion.

Question 19

Answer 19

A??

Question 20

Answer 20

B

Catalysts work by lowering the activation energy of a reaction, which increases the reaction rate without being consumed in the process. Without a catalyst, the reaction would proceed at a slower rate because the energy barrier to start the reaction (activation energy) would be higher.

Question 21

The purpose of a catalyst is to
a. increase the activation energy
b. increase the energy released by the reaction
c. reduce the net energy released by the reaction
d. provide an alternative energy pathway for the reaction

Answer 21

D, The purpose of a catalyst is to provide an alternative energy pathway with a lower activation energy, allowing the reaction to proceed faster without being consumed in the process.

Question 22

When a catalyst is used in a reaction the enthalpy change for the reaction
a. stays the same
b. becomes more exothermic
c. becomes more endothermic
d. increases or decreases, depending on the catalyst used

Answer 22

A, When a catalyst is used in a reaction, it does not affect the overall enthalpy change (ΔH) of the reaction. Catalysts only lower the activation energy, speeding up the rate of the reaction, but the energy difference between the reactants and products (enthalpy change) remains the same.

Question 23

Answer 23

A
Manipulated variable: This is the variable that the experimenter changes or controls directly. In this case, the type of fuel (methanol or ethanol) is being changed to compare the enthalpy changes.
Responding variable: This is the variable that changes in response to the manipulated variable. Here, the temperature change is what is being measured after burning each fuel.
Therefore, the correct answer is:
a. Manipulated variable is the type of fuel, and the responding variable is the temperature change.

Question 24

Answer 24

C

Question 25

Answer 25

D, In an endothermic reaction, energy is absorbed, resulting in products that have higher energy than the reactants. This is indicated by the products being at a higher energy level than the reactants in the diagram, which would correspond to a positive ΔH.
The reaction is endothermic.
ΔH is positive.
The difference between the products (IV) and the reactants (I) gives the value of ΔH.
This means the correct answer is Row D: ΔH is positive, and it is the difference between I and IV.