Question 1

Which of the following best describes the relationship between internal energy ($$E) $$and enthalpy ($$H) $$for a chemical system at constant pressure?

Accepted Answer

$$H = E + PV$$

Question 2

A gas expands against a constant external pressure. Which equation correctly represents the work ($$w) $$done by the system?

Accepted Answer

$$w = -P_{ext} \Delta V$$

Question 3

Which of the following statements about endothermic and exothermic reactions is correct?

Accepted Answer

Endothermic reactions absorb heat from the surroundings, while exothermic reactions release heat to the surroundings.

Question 4

Given the reaction: $$\mathrm{CH_4$(g) + 2 O_2$(g) \rightarrow CO_2$(g) + 2 H_2O(l)}$$ with $$\Delta H = -890\ \mathrm{kJ}$$, what does the negative sign indicate?

Accepted Answer

The reaction is exothermic and releases heat.

Question 5

Which of the following is true about the internal energy ($$E) of a $$system?

Accepted Answer

It is the sum of all kinetic and potential energies of all components in the system.

Question 6

If a system absorbs 100 J of heat and does 40 J of work on the surroundings, what is the change in internal energy ($$\Delta E$$)?

Accepted Answer

$$\Delta E = 60\ \mathrm{J}$$

Question 7

Which of the following best describes an open system in thermodynamics?

Accepted Answer

A system that can exchange both energy and matter with its surroundings.

Question 8

In the context of chemical reactions, breaking chemical bonds is always:

Accepted Answer

Endothermic, because energy is required to break bonds.

Question 9

Which sign convention is correct for heat ($$q) $$and work ($$w) in $$the First Law of Thermodynamics?

Accepted Answer

$$q \u003e 0$$ means the system gains heat; $$w \u003e 0$$ means work is done on the system.

Question 10

A reaction occurs at constant pressure and results in a decrease in volume. Which of the following is true about the sign of $$w ($$work)?

Accepted Answer

$$w is $$positive because work is done on the system.

Question 11

Which equation correctly relates the change in enthalpy ($$\Delta H) to $$the change in internal energy ($$\Delta E) at $$constant pressure?

Accepted Answer

$$\Delta H = \Delta E + P\Delta V$$

Question 12

Which of the following best describes the surroundings in a thermodynamic experiment involving a gas in a piston?

Accepted Answer

Everything outside the gas, including the piston and cylinder.

Question 13

Which of the following is a correct statement about the enthalpy of reaction ($$\Delta H_{rxn}$$)?

Accepted Answer

$$\Delta H_{rxn} is $$the heat exchanged at constant pressure.

Question 14

A chemical reaction absorbs 250 kJ of heat from the surroundings and the system does 50 kJ of work on the surroundings. What is $$\Delta E$$ for the system?

Accepted Answer

$$\Delta E = 200\ \mathrm{kJ}$$

Question 15

Which of the following best describes an isolated system?

Accepted Answer

A system that cannot exchange energy or matter with its surroundings.

Question 16

Which of the following is true for an exothermic reaction?

Accepted Answer

The products have lower enthalpy than the reactants.

Question 17

Which of the following is a correct graphical representation of an endothermic reaction?

Accepted Answer

The products are at a higher energy level than the reactants.

Question 18

Which of the following is a correct statement about the energy changes when a cyclist climbs and descends a hill, as shown in the first image?

Accepted Answer

Kinetic energy is converted to potential energy while climbing, and potential energy is converted back to kinetic energy while descending.

Internal Energy and Enthalpy in Chemical Systems

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