Q: It takes 12.9 hours for a 0.75 mol sample of Ar to effuse through pores in a balloon. What is the rate of effusion of Ar?

$$\text{Rate} = \frac{0.75\ \mathrm{mol}}{12.9\ \mathrm{hr}} = 0.058\ \mathrm{mol/hr}$$

Q: An unknown gas effuses through a pinhole 1.24 times as fast as Xe. What is the molar mass of the unknown gas?

$$M_{\text{unknown}} = \frac{M_{Xe}}{(1.24)^2$} = 108\ \mathrm{g/mol}$$

Q: An unknown gas effuses through a pinhole 0.411 times as fast as Ne. What is the molar mass of the unknown gas?

$$M_{\text{unknown}} = M_{Ne} \div (0.411)^2$ = 122\ \mathrm{g/mol}$$

Question 1

Which of the following best describes an 'exchange' reaction in aqueous solution?

Accepted Answer

A reaction where ions from two compounds swap partners, forming two new compounds.

Question 2

What is the chemical term for a product that 'falls out of solution' during a reaction?

Accepted Answer

Precipitate

Question 3

When aqueous solutions of $$\mathrm{$$AlCl_3$$}$$ and $$\mathrm{K_2S}$$ are mixed, what is the net ionic equation for the reaction?

Accepted Answer

$$2\mathrm{Al$$^{3+}$$}(aq) + 3\mathrm{S$$^{2-}$$}(aq) \rightarrow \mathrm{Al_2S_3}(s)$$

Question 4

How many moles of $$\mathrm{$$HClO_4$$}$$ are needed to neutralize 1 mole of $$\mathrm{Ca(OH)_2}$$?

Accepted Answer

2 moles

Question 5

What is the chemical formula of the neutral salt formed when $$\mathrm{Ca(OH)_2}$$ reacts with $$\mathrm{$$HClO_4$$}$$?

Accepted Answer

$$\mathrm{Ca($$ClO_4$$)_2}$$

Question 6

An inflated balloon has a volume of 5.45 L at sea level (1.00 atm) and is allowed to ascend until the pressure is 0.21 atm. The temperature falls from 32°C to 15°C. What is the final volume of the balloon? (Use the ideal gas law.)

Accepted Answer

$$V_2$$ = \frac{$$P_1$$ $$V_1$$ $$T_2$$}{$$P_2$$ $$T_1$$}$$, so V_2$ \approx 27.2\ \mathrm{L}$$

Question 7

A steel cylinder contains 6.0 mol of Argon gas at 14°C and 3.6 atm. After some Ar is used, the pressure is 1.2 atm at the same temperature. How many mol of Ar remain in the tank?

Accepted Answer

2.0 mol

Question 8

What is the molar volume of any gas at STP (standard temperature and pressure)?

Accepted Answer

$$22.4\ \mathrm{L/mol}$$

Question 9

A cylinder contains 2.50 g of He, 3.75 g of Ne, and an unknown amount of Ar. The mole fraction of Ne in the mixture is 0.107. What is the mass of Ar in the mixture?

Accepted Answer

25.6 g

Question 10

Given the partial pressure of Ne is 216 torr, and the total pressure in the cylinder is 1192.5 torr, what is the mole fraction of Ne?

Accepted Answer

$$X_{Ne} = \frac{216}{1192.5} = 0.181$$

Question 11

Consider the reaction: $$4\mathrm{NH_3$}(g) + 5\mathrm{O_2$}(g) \rightarrow 4\mathrm{NO}(g) + 6\mathrm{H_2O}(g). $$How many L of $$\mathrm{NH_3$} at 850$$°C and 5.00 atm are required to react with 0.50 mol of $$\mathrm{O_2$}$$?

Accepted Answer

2.24 L

Question 12

Detonation of nitroglycerin ($$\mathrm{C_3H_5O_3N_3}) $$proceeds as follows: $$4\mathrm{C_3H_5O_3N_3}(l) \rightarrow 12\mathrm{CO_2$}(g) + 10\mathrm{H_2O}(g) + 6\mathrm{N_2$}(g) + O_2$(g). If $$the products are trapped in a 5.0 L flask at 23°C, what will be the total pressure from the gases after the reaction?

Accepted Answer

$$P = \frac{nRT}{V}$$, $$n = 29$$ mol, $$P \approx 136$$ atm

Question 13

It takes 12.9 hours for a 0.75 mol sample of Ar to effuse through pores in a balloon. What is the rate of effusion of Ar?

Accepted Answer

$$	ext{Rate} = \frac{0.75\ \mathrm{mol}}{12.9\ \mathrm{hr}} = 0.058\ \mathrm{mol/hr}$$

Question 14

An unknown gas effuses through a pinhole 1.24 times as fast as Xe. What is the molar mass of the unknown gas?

Accepted Answer

$$M_{	ext{unknown}} = \frac{M_{Xe}}{(1.24)^2$} = 108\ \mathrm{g/mol}$$

Question 15

An unknown gas effuses through a pinhole 0.411 times as fast as Ne. What is the molar mass of the unknown gas?

Accepted Answer

$$M_{	ext{unknown}} = M_{Ne} \div (0.411)^2$ = 122\ \mathrm{g/mol}$$

General Chemistry Study Guide: Chemical Reactions, Solutions, and Gas Laws

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