Q: For the reaction $$4 NH_3$(g) + 5 O_2$(g) \rightarrow 4 NO(g) + 6 H_2O(g)$$, which of the following is a correct rate equation?

$$\text{rate} = -\frac{1}{4} \frac{\Delta [NH_3$]}{\Delta t}$$

Question 1

A diver is at a depth where the pressure is 14.8 atm. The Henry’s Law constant for nitrogen ($$N_2) is$$ $$1.67 	imes 10$$^{-4}$$ M/atm. What is the solubility of nitrogen in water at this pressure?

Accepted Answer

$$2.47 	imes 10$$^{-3}$$ M

Question 2

Which of the following changes will increase the solubility of a gas in water?

Accepted Answer

Increase the pressure of the gas above the solution and decrease the temperature of the water.

Question 3

A sample of iron with a mass of 1.03 kg requires 254 kJ of heat to melt completely. What is the enthalpy of fusion ($$\Delta H_{fus}) of $$iron in kJ/mol? (Fe = 55.85 g/mol)

Accepted Answer

$$13.8 kJ/$$mol

Question 4

When ammonium chloride ($$NH_4Cl) is $$dissolved in water, the test tube feels cold. Which of the following statements is correct?

Accepted Answer

The process is endothermic because the system absorbs heat from the surroundings.

Question 5

7.50 g of sodium acetate ($$CH_3COONa) is $$added to 100.0 mL of water in a coffee cup calorimeter. The temperature of the solution increases from $$20.00^\circ C to$$ $$23.52^\circ C. If $$the specific heat of the solution is $$4.184 J/(g$\cdot^\circC$$), what is the heat absorbed by the solution ($$q_{solution}$$)? (Assume total mass = 107.5 g)

Accepted Answer

$$1.57 	imes 10^3$ J

Question 6

The combustion of ethanol is given by:

$$C_2H_6O(l) + 3O_2(g) \rightarrow 2CO_2(g) + 3H_2O(l)$$, $$\Delta H = -1367 kJ

$$How much heat is released when 10.0 g of ethanol is combusted? (Molar mass of ethanol = 46.07 g/mol)

Accepted Answer

$$-297 kJ$$

Question 7

Which statement best describes the difference between $$q$$ and $$\Delta H$$ for a chemical reaction at constant pressure?

Accepted Answer

$$q is $$the heat exchanged, while $$\Delta H is $$the heat exchanged at constant pressure and equals $$q$$ only under those conditions.

Question 8

Use Hess’s Law and the following equations to calculate $$\Delta H$$ for the reaction:

$$NO_2(g) + CO(g$$) \rightarrow NO(g) + $$CO_2(g$$)$$

Given:
2 NO(g$$) + $$O_2(g$$) \rightarrow 2 $$NO_2(g$$)$$ $$\Delta H = -113.1$$ kJ
2 CO(g$$) + $$O_2(g$$) \rightarrow 2 $$CO_2(g$$)$$ $$\Delta H = -566.0$$ kJ

Accepted Answer

$$-112.5 kJ$$

Question 9

When magnesium metal is burned in a pure carbon dioxide atmosphere, the reaction is:

$$2 Mg(s) + CO_2$(g) \rightarrow 2 MgO(s) + C(s)$$

Given $$\Delta H_f$$ for $$CO_2(g) = -393.5$ kJ/mol and $$\Delta H_f$$ for $$MgO(s) = -601.6$$ kJ/mol, what is $$\Delta H_{rxn}$$ for the reaction? Is it exothermic or endothermic?

Accepted Answer

$$-409.7 kJ$$, exothermic

Question 10

Calculate the enthalpy of combustion of ethane using the following average bond enthalpy values:
C–H: 413 kJ/mol, C–C: 347 kJ/mol, O=O: 498 kJ/mol, C=O: 799 kJ/mol, O–H: 463 kJ/mol

$$2CH_3CH_3(g) + 7O_2(g) \rightarrow 4CO_2(g) + 6H_2O(l)$$

What does the $$\Delta H$$ value tell you about the stability of the reactant bonds compared to the products?

Accepted Answer

The negative $$\Delta H$$ indicates that the bonds in the products are more stable than those in the reactants.

Question 11

Which of the following best describes the function of a coffee cup calorimeter?

Accepted Answer

It measures the heat change of a reaction at constant pressure.

Question 12

For the reaction $$4 NH_3$(g) + 5 O_2$(g) \rightarrow 4 NO(g) + 6 H_2O(g)$$, which of the following is a correct rate equation?

Accepted Answer

$$	ext{rate} = -\frac{1}{4} \frac{\Delta [NH_3$]}{\Delta t}$$

Question 13

The rate law for the reaction $$2 $$MnO_4$$^- + 5 H_2C_2O_4 + 6 H^+ ightarrow 2 Mn$$^{2+}$$ + 10 CO_2$ + 8 H_2O is$$ $$	ext{rate} = k[$$MnO_4$$^-][H_2C_2O_4][H^+]. $$What is the overall order of the reaction?

Accepted Answer

3

Question 14

For the same reaction and rate law as above, how would the rate change if the $$[$$MnO_4$$^-]$$ concentration was doubled?

Accepted Answer

The rate would double.

Question 15

For the same reaction and rate law as above, how would the rate change if all reactant concentrations were doubled?

Accepted Answer

The rate would increase by a factor of 8.

Question 16

In a reaction $$A \rightarrow$$ Products, the concentration of $$A$$ drops from 1.5 M to 0.75 M in 10 seconds, and from 0.75 M to 0.375 M in the next 10 seconds. What is the order of the reaction?

Accepted Answer

First order

Question 17

Calculate the average rate of disappearance of $$A in $$the first 10 seconds if $$[A]$$ decreases from 1.5 M to 0.75 M.

Accepted Answer

$$0.075 M/s$$

Question 18

Which of the following best describes how increasing the concentration of reactants affects the rate of a chemical reaction?

Accepted Answer

It increases the rate because more reactant particles lead to more frequent collisions.

Question 19

A bomb calorimeter is used to measure the heat of combustion of a fuel. Which of the following statements is correct?

Accepted Answer

It measures the heat change at constant volume.

General Chemistry Exam 2 Review: Solutions, Thermochemistry, and Kinetics

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