Q: Convert a pressure of 24.9 inHg to mmHg and atm. (1 atm = 760 mmHg, 1 inHg = 25.4 mmHg)

$$24.9 \times 25.4 = 632.46$$ mmHg and $$\frac{632.46}{760} = 0.832$$ atm

Q: A sample of nitrogen dioxide gas at 130°C and 315 torr occupies a volume of 1750 mL. What will the gas pressure be if the volume is reduced to 320 mL at 130°C?

$$P_2$$ = $$P_1$$ \frac{$$V_1$$}{$$V_2$$} = 315 \times \frac{1750}{320} = 1,721$$ torr

Question 1

Which of the following best describes the SI unit for pressure and its origin?

Accepted Answer

The SI unit for pressure is the pascal (Pa), named after the French mathematician Blaise Pascal.

Question 2

A 5.0 L container of gas is expanded to 100.0 L at constant temperature. What happens to the pressure inside the container?

Accepted Answer

It will decrease.

Question 3

Convert a pressure of 24.9 inHg to mmHg and atm. (1 atm = 760 mmHg, 1 inHg = 25.4 mmHg)

Accepted Answer

$$24.9 	imes 25.4 = 632.46$$ mmHg and $$\frac{632.46}{760} = 0.832$$ atm

Question 4

Given 25.0 g dichloromethane (CH$$_2Cl$_2) $$dissolved in 125 g H$$_2O$$, what is the mole fraction of dichloromethane? (Molar masses: CH$$_2Cl$_2 = 84.93 g/$$mol, H$$_2O = 18.02 g/$$mol)

Accepted Answer

$$X_{CH_2Cl_2} = \frac{0.294}{0.294 + 6.94} = 0.040 ($$rounded to 3 decimals)

Question 5

A sample of neon gas exerts a pressure of 1.85 atm inside a cylinder. Some nitrogen gas is also present at a pressure of 500 torr. What is the total pressure inside the cylinder? (1 atm = 760 torr)

Accepted Answer

$$P_{total} = 1.85 + \frac{500}{760} = 2.51$$ atm

Question 6

If 12.0 g helium and 20.0 g oxygen are placed inside a 5.0 L cylinder at 30°C, what is the partial pressure of the helium gas? (Molar mass He = 4.00 g/mol, R = 0.08206 L·atm/mol·K)

Accepted Answer

$$n_{He} = \frac{12.0}{4.00} = 3.00$$ mol; $$T = 303 K$$; $$P_{He} = \frac{3.00 	imes 0.08206 	imes 303}{5.0} = 14.9$$ atm

Question 7

A container has 16.7 g O$$_2$$, 8.1 g H$$_2$$, and 35.2 g N$$_2$$ and contains a total pressure of 0.83 atm. What is the mole fraction of O$$_2$$ and its partial pressure? (Molar masses: O$$_2 = 32.00 g/$$mol, H$$_2 = 2.02 g/$$mol, N$$_2 = 28.02 g/$$mol)

Accepted Answer

$$n_{O_2$} = 0.522$$ mol; $$n_{H_2$} = 4.01$$ mol; $$n_{N_2$} = 1.26$$ mol; $$X_{O_2$} = \frac{0.522}{0.522+4.01+1.26} = 0.085$$; $$P_{O_2$} = 0.085 	imes 0.83 = 0.070$$ atm

Question 8

A 500 mL container at a pressure of 600 mmHg possesses 23.9 g nitrogen gas at 50°C. Determine the correct units needed for the Ideal Gas Law.

Accepted Answer

Pressure in atm, volume in liters, temperature in Kelvin, amount in moles

Question 9

How many moles of NH$$_3$$ are contained in a 25.0 L tank at 190°C and 5.20 atm? (R = 0.08206 L·atm/mol·K)

Accepted Answer

$$T = 190 + 273 = 463 K$$; $$n = \frac{PV}{RT} = \frac{5.20 	imes 25.0}{0.08206 	imes 463} = 3.41$$ mol

Question 10

A sample of sulfur hexachloride gas occupies 8.30 L at 202°C. Assuming pressure remains constant, what temperature (in °C) is needed to decrease the volume to 5.25 L?

Accepted Answer

$$\frac{V_1$}{T_1$} = \frac{V_2$}{T_2$}$$; $$T_2$$ = \frac{5.25 	imes (202+273)}{8.30} = 189$$ K; T_2$ = 189 - 273 = -84$$°C

Question 11

A sample of nitrogen dioxide gas at 130°C and 315 torr occupies a volume of 1750 mL. What will the gas pressure be if the volume is reduced to 320 mL at 130°C?

Accepted Answer

$$P_2$$ = $$P_1$$ \frac{$$V_1$$}{$$V_2$$} = 315 	imes \frac{1750}{320} = 1,721$$ torr

Question 12

A cylinder with a movable piston contains 0.615 moles of gas and has a volume of 295 mL. What will its volume be if 0.103 moles of gas escaped, assuming temperature and pressure remain constant?

Accepted Answer

$$V_2$$ = $$V_1$$ \frac{$$n_2$$}{$$n_1$$} = 295 	imes \frac{0.512}{0.615} = 245$$ mL

Question 13

On most spray cans, it is advised to never expose them to fire. A spray can is used until all that remains is the propellant gas, which has a pressure of 1350 torr at 25°C. If the can is then thrown into a fire at 455°C, what will be the pressure (in torr) in the can?

Accepted Answer

$$P_2$$ = $$P_1$$ \frac{$$T_2$$}{$$T_1$$} = 1350 	imes \frac{728}{298} = 3,295$$ torr

Question 14

If the number of moles (n) inside a container were tripled while keeping the pressure (P) constant, what will happen to the volume (V)?

Accepted Answer

It will triple.

Question 15

Which of the following graphs best represents the relationship between the partial pressure of a gas (P) and the number of moles of that gas (n) in a mixture?

Accepted Answer

A straight line passing through the origin, showing direct proportionality.

Question 16

Which Chemistry Gas Law would be used to justify the following scenario: A 10.0 L cylinder with a movable piston contains 10.0 g of xenon gas. When an additional 10.0 g of xenon gas are added, the volume increases.

Accepted Answer

Avogadro's Law

Question 17

A 10.0 L cylinder with a movable piston exerts 3.00 atm of pressure. What will happen to the pressure if the volume of the container increases to 20.0 L?

Accepted Answer

It will decrease by half.

Question 18

A sealed container with a movable piston contains a gas with a pressure of 1380 torr, a volume of 820 mL, and a temperature of 31°C. What would the volume be if the new pressure is now 2.83 atm, while the temperature decreased to 25°C? (1 atm = 760 torr)

Accepted Answer

$$P_1$$ = \frac{1380}{760} = 1.82$$ atm; T_1$ = 304 K$$; $$T_2 = 298$ K; V_2$ = V_1$ \frac{P_1$}{P_2$} \frac{T_2$}{T_1$} = 820 	imes \frac{1.82}{2.83} 	imes \frac{298}{304} = 424 mL$$

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