Question 1

Which of the following statements about enthalpy ($$\Delta H) is $$correct for a chemical reaction occurring at constant pressure?

Accepted Answer

$$\Delta H is $$always equal to the heat absorbed or released by the system.

Question 2

A reaction has $$\Delta H = -150 kJ $$and $$\Delta S = -200 J/K. At $$what temperature (in K) does the reaction change from spontaneous to non-spontaneous?

Accepted Answer

$$T = 750 K$$

Question 3

Which of the following best describes the relationship between bond enthalpy and bond strength?

Accepted Answer

Higher bond enthalpy corresponds to stronger bonds.

Question 4

Given the reaction: $$2H_2(g) + O_2$(g) \rightarrow 2H_2O(l)$$, which statement is true regarding the enthalpy change?

Accepted Answer

The reaction is exothermic and $$\Delta H is $$negative.

Question 5

A 5.00 g sample of CaCl$$_2 is $$added to 100.0 g of water in a calorimeter, causing the temperature to increase by 2.50 $$^\circC. If $$the specific heat capacity of water is $$4.18 J/g$\cdotK$$, what is the heat absorbed by the water?

Accepted Answer

$$Q = 1045 J$$

Question 6

Which of the following is NOT a correct statement about standard enthalpy of formation ($$\Delta H_f^\circ$$)?

Accepted Answer

It is always positive.

Question 7

Calculate the standard enthalpy change ($$\Delta H^\circ) $$for the reaction: $$2SO_2(g) + O_2$(g) \rightarrow 2SO_3(g)$$, given $$\Delta H_f^\circ(SO_2$) = -296.8 kJ/$$mol and $$\Delta H_f^\circ(SO_3$) = -395.7 kJ/$$mol.

Accepted Answer

$$\Delta H^\circ = -197.8 kJ$$

Question 8

Which of the following reactions will have the largest difference between $$\Delta H$$ and $$q$$ for the system?

Accepted Answer

A reaction that produces a large amount of gas.

Question 9

If the molar mass of propane ($$C_3H_8) is 44.1 g/$$mol, what is the mean free path (in pm) of propane molecules at STP (0 $$^\circC $$and 1 atm) given a molecular diameter of $$4.3 	imes 10$$^{-10}$$ m?

Accepted Answer

$$\lambda = 68 pm$$

Question 10

Which statement best explains why hydrogen bonding leads to higher boiling points in water compared to methane?

Accepted Answer

Hydrogen bonds are much stronger than London dispersion forces present in methane.

Question 11

Which of the following is the correct expression for calculating the work done by a gas during expansion at constant pressure?

Accepted Answer

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

Question 12

A reaction occurs in a bomb calorimeter. Which of the following statements is true?

Accepted Answer

The reaction occurs at constant volume, so $$q_v = \Delta U.$$

Question 13

Which of the following is a correct statement about entropy ($$\Delta S$$)?

Accepted Answer

Entropy increases when a solid melts to a liquid.

Question 14

Given the following reactions and their enthalpy changes:
$$1) 2Fe(s) + 3Cl_2(g) \rightarrow 2FeCl_3(s), \Delta H_1$ = -824.2 kJ/$$mol$$
2$$) $$FeCl_3(s) + 3H_2O(l$$) \rightarrow Fe_2O_3(s) + 6HCl(aq), \Delta $$H_2 = -448.1$ kJ/mol$$
Calculate the standard molar enthalpy change for the reaction:
$$2Fe(s) + 3Cl_2(g) + 3H_2O(l) \rightarrow Fe_2O_3(s) + 6HCl(aq)$$

Accepted Answer

$$\Delta H = -1272.3 kJ/$$mol

Question 15

Which of the following compounds has the highest lattice enthalpy?

Accepted Answer

MgO

Question 16

Which of the following is true about the sign of $$\Delta H$$ for a combustion reaction?

Accepted Answer

$$\Delta H is $$negative because energy is released.

Question 17

Which of the following processes is associated with the largest increase in entropy?

Accepted Answer

Sublimation of dry ice ($$CO_2(s$$) \rightarrow $$CO_2(g$$)$$)

Question 18

Which of the following is the correct formula for calculating the change in internal energy ($$\Delta U) of a $$system?

Accepted Answer

$$\Delta U = q + w$$

Question 19

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

Accepted Answer

It is zero for elements in their standard states.

Thermochemistry, Calorimetry, and Enthalpy: Practice Quiz Study Notes

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