Q: Which of the following is the correct formula for calculating the enthalpy change of a reaction using heats of formation?

$$\Delta H = \sum n \Delta H_{f}(\text{products}) - \sum n \Delta H_{f}(\text{reactants})$$

Question 1

Which of the following best explains why O$$_2(g) $$and N$$_2(g) $$are not considered greenhouse gases?

Accepted Answer

They do not absorb infrared radiation due to lack of symmetry breaking in their vibrational modes.

Question 2

A chemist mixes 2.0 mol of propane (C$$_3H$_8) $$with 10.0 mol of O$$_2$$ for a combustion reaction. The balanced equation is: $$\mathrm{C_3H_8 + 5O_2 \rightarrow 3CO_2 + 4H_2O}. $$What is the limiting reactant?

Accepted Answer

O$$_2$$

Question 3

Which equation describes the relationship between absorbance and concentration according to Beer's Law?

Accepted Answer

$$A = \epsilon b c$$

Question 4

A solution is prepared by dissolving 0.50 mol NaCl in enough water to make 1.0 L of solution. What is the molarity of the solution?

Accepted Answer

$$0.50\ \mathrm{M}$$

Question 5

Which of the following is a correct net ionic equation for the reaction between AgNO$$_3$$ and NaCl in aqueous solution?

Accepted Answer

$$\mathrm{Ag^+ (aq) + Cl^- (aq) \rightarrow AgCl (s)}$$

Question 6

Which of the following statements about water is TRUE and helps explain its central role in biological and environmental systems?

Accepted Answer

Water has a high heat capacity, allowing it to moderate temperature changes.

Question 7

A student mixes 50.0 mL of 0.10 M HCl with 50.0 mL of 0.10 M NaOH. What is the total number of moles of water produced in the neutralization reaction?

Accepted Answer

$$0.005\ \mathrm{mol}$$

Question 8

Which of the following is the correct definition of a formation reaction?

Accepted Answer

A reaction in which one mole of a compound is formed from its elements in their standard states.

Question 9

Which of the following is a strong electrolyte when dissolved in water?

Accepted Answer

NaCl

Question 10

A reaction has $$q = -150\ \mathrm{J}$$ and $$w = +50\ \mathrm{J}. $$What is $$\Delta E$$ for the system?

Accepted Answer

$$-100\ \mathrm{J}$$

Question 11

Which of the following best describes an exothermic reaction?

Accepted Answer

A reaction in which $$\Delta H is $$negative and heat is released to the surroundings.

Question 12

Which of the following is the correct formula for calculating the enthalpy change of a reaction using heats of formation?

Accepted Answer

$$\Delta H = \sum n \Delta H_{f}(	ext{products}) - \sum n \Delta H_{f}(	ext{reactants})$$

Question 13

Which of the following is a correct example of a precipitation reaction?

Accepted Answer

$$\mathrm{$$BaCl_2$$ (aq) + Na_2SO_4 (aq) \rightarrow $$BaSO_4$$ (s) + 2NaCl (aq)}$$

Question 14

Which of the following statements about oxidation numbers is correct?

Accepted Answer

The oxidation number of oxygen in most compounds is $$-2.$$

Question 15

A 100.0 g sample of water absorbs 4200 J of heat. If the specific heat of water is $$4.18\ \mathrm{J\ g$$^{-1}$$\ ^\circ C$$^{-1}$$}$$, what is the temperature change?

Accepted Answer

$$10.0\ ^\circ \mathrm{C}$$

Question 16

Which of the following is a state function?

Accepted Answer

Enthalpy ($$H)$$

Question 17

Which of the following is TRUE about geologic hydrogen as an energy source?

Accepted Answer

It can be obtained by drilling or mining underground where hydrogen forms naturally.

Question 18

Which of the following is the correct expression for Coulomb’s Law describing electrostatic potential energy?

Accepted Answer

$$E_{el} = \dfrac{kQ_1Q_2}{r}$$

Question 19

Which of the following is the correct definition of a reducing agent?

Accepted Answer

A substance that donates electrons and is itself oxidized.

Comprehensive Study Guidance for Chemistry 1770 Exam #3

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