Question 1

Which of the following statements best describes a state function in thermochemistry?

Accepted Answer

A property that depends only on the initial and final states of a system, not on the path taken.

Question 2

A balloon filled with 10.0 mol of He (C = 20.8 J/K) has a volume of 2.00 L at 20.0°C and 1.00 atm. At constant P, the volume increased to 50.0 L and the temperature increased to 25.0°C. What is the correct formula to calculate the change in internal energy ($$\Delta E) $$for this process?

Accepted Answer

$$\Delta E = q + w$$

Question 3

Which equation correctly represents the work done by a gas during expansion at constant pressure?

Accepted Answer

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

Question 4

In calorimetry, which formula is used to calculate the heat absorbed or released by a substance?

Accepted Answer

$$q = m c \Delta T$$

Question 5

Which of the following best describes the difference between kinetic and potential energy in the context of chemical systems?

Accepted Answer

Kinetic energy is due to motion, while potential energy is due to position or composition.

Question 6

Which statement about the First Law of Thermodynamics is correct?

Accepted Answer

Energy cannot be created or destroyed, but it can be converted to different forms.

Question 7

A coffee-cup calorimeter is used to measure the heat flow of a reaction at constant pressure. Which equation should be used to calculate the heat of the reaction?

Accepted Answer

$$q_{reaction} = -q_{solution}$$

Question 8

Which of the following is true regarding enthalpy ($$H) $$and its change ($$\Delta H) in a $$chemical reaction?

Accepted Answer

$$\Delta H is $$the heat exchanged at constant pressure.

Question 9

Given the reaction: $$2H_2(g) + O_2$(g) \rightarrow 2H_2O(l)$$, $$\Delta H = -285.8 kJ. $$What does the negative sign of $$\Delta H$$ indicate?

Accepted Answer

The reaction is exothermic and releases heat to the surroundings.

Question 10

Which rule of thermochemistry allows you to reverse a chemical equation and change the sign of $$\Delta H$$?

Accepted Answer

If a reaction is reversed, the sign of $$\Delta H is $$also reversed.

Question 11

Which of the following best describes Hess's Law?

Accepted Answer

The enthalpy change for a reaction is the same whether it occurs in one step or in a series of steps.

Question 12

Which equation is used to calculate the standard enthalpy of formation ($$\Delta H_f^\circ) $$for a compound?

Accepted Answer

$$\Delta H_f^\circ = \sum \Delta H_f^\circ (products) - \sum \Delta H_f^\circ (reactants)$$

Question 13

A bomb calorimeter is best used for which type of reactions?

Accepted Answer

Reactions involving gases, high temperature, or liquids that dissolve hydrocarbon.

Question 14

Which of the following is NOT a correct statement about the measurement of heat flow using calorimetry?

Accepted Answer

Calorimetry cannot be used to measure the enthalpy change of a reaction.

Question 15

If the specific heat capacity ($$c) of a $$metal is 0.385 J/g·K, what is the heat required to raise the temperature of 50.0 g of the metal by 25.0 K?

Accepted Answer

$$q = 0.385 	imes 50.0 	imes 25.0 = 481.25 J$$

Question 16

Which of the following is a correct application of the First Law of Thermodynamics to a chemical system?

Accepted Answer

The change in internal energy of a system equals the heat added to the system plus the work done on the system.

Question 17

Which of the following is true about the sign convention for heat ($$q) in $$thermochemistry?

Accepted Answer

Heat absorbed by the system is positive, heat released by the system is negative.

Question 18

Which of the following is a correct statement about standard enthalpy of formation ($$\Delta H_f^\circ$$)?

Accepted Answer

It refers to the enthalpy change when one mole of a compound is formed from its elements in their standard states.

Question 19

Which of the following is a correct use of a thermochemical equation?

Accepted Answer

It must specify the physical states of all reactants and products.

Energy, Enthalpy, and Thermochemistry: Study Notes

Guida di studio - Domande di pratica

Study guide - Flashcard