Unit 11 - Gases

Question 1

Boyle’s Law

Answer 1

The pressure and volume of a gas are inversely proportional at a constant temperature.

P₁V₁ = P₂V₂

Question 2

Charles’ Law

Answer 2

The volume of a gas is directly proportional with the KELVIN temperature at a constant pressure.

V₁T₂ =V₂T₁

Question 3

Kinetic Molecular Theory of Gases

Answer 3

1. Gases consist of tiny particles.
2. These particles are so small, their volume can be assumed to be negligible (zero).
3. The particles are in constant, random motion, colliding with the walls of the container. These collisions with the walls cause the pressure exerted by the gas.
4. The particles are assumed not to attract or repel each other.
5. The kinetic energy of the particles is directly proportional to the Kelvin temperature of the gas.

(As the temperature increases the energy increases)

Question 4

Standard Temperature & Pressure (STP) - a shorthand method that can be used when writing word problems.

Answer 4

Question 5

Barometer

Answer 5

Measures atomospheric pressure.

Question 6

Combined Gas Law

Answer 6

P₁V₁T₂ = P₂V₂T₁

Question 7

Ideal Gas Law

Answer 7

Question 8

Dalton’s Law of Partial Pressures

Answer 8

Question 9

Molar Volume of a Gas

Answer 9

1 mole of any gas at STP = 22.4 Liters

Question 10

Kinetic Energy

Answer 10

The energy an object has due to its motion.

Question 11

Atmospheric Pressure

Answer 11

Pressure resulting from the collisions of atoms and molecules with objects.

Question 12

What are the conversions between pressure units? (What amount of atm equals what amount of kPa, psi, torr, etc)

Answer 12

1 atm = 760 torr = 760 mmHg = 101.3 kPa

Question 13

If 2.5g of sulfur hexafluoride is introduced to an evacuated 500.0mL container at 83*C, what is the pressure, in atmospheres, inside the container?

Answer 13

PV = nRT

2.5g SF₆ (1mole SF₆/ 146.08 g SF₆) = 0.017 moles SF₆

P = (nRT)/V

P =[ (0.017 moles)x(0.08205746 L atm/K mol)x(83+273K)/(.5 L)

P =0.99atm

Question 14

If the total pressure of a two gas system is 100 torr and the partial pressure of one gas is 70 torr, what is the pressure of the other gas?

Answer 14

P_other = 30 torr

Question 15

Gases deviate most from ideal behavior under conditions of very ______ temperature and very _______ pressure

Answer 15

low; high

Question 16

According to _____________ law, pressure and volume are ______________ proportional provided all other factors remain constant. Mathematically, this means that their ____________ is a constant.

Answer 16

Boyle’s; inversely; temperature

Question 17

If pressure is constant, the volume of a sample of gas _____________ as temperature increases.

Answer 17

increases

Question 18

At constant pressure, the volume of a sample of gas is ___________ proportional to temperature as measured on the ____________ temperature scale

Answer 18

directly; Kelvin

Question 19

A balloon with a volume of 2.0 L is filled with a gas at 3 atmospheres. If the pressure is reduced to 0.5 atmospheres without a change in temperature, what would be the volume of the balloon?

Answer 19

Since the temperature does not change, Boyle’s law can be used. Boyle’s gas law can be expressed as:

P_iV_i = P_fV_f (i=initial and f=final)

To find the final volume, solve the equation for Vf:

Vf = PiVi/Pf

Vi = 2.0 L
Pi = 3 atm
Pf = 0.5 atm

Vf = (2.0 L)(3 atm)/(0.5 atm)
Vf = 6 L/0.5
Vf = 12 L

Answer:

The volume of the balloon will expand to 12 L.

Question 20

A 600 mL sample of nitrogen is heated from 27 °C to 77 °C at constant pressure. What is the final volume?

Answer 20

The first step to solving gas law problems should be converting all temperatures to absolute temperatures. This is the most common place mistakes are made in this type of homework problem.

K = 273 + °C
Ti = initial temperature = 27 °C
K = 273 + 27
K_i = 300 K

Tf = final temperature = 77 °C
K = 273 + 77
K_f = 350 K

The next step is to use Charles’ law to find the final volume. Charles’ law is expressed as:

ViTf = VfTi

where
Vi and Ti is the initial volume and temperature
Vf and Tf is the final volume and temperature

Solve the equation for Vf:

Vf = ViTf/Ti

Enter the known values and solve for Vf.

Vf = (600 mL)(350 K)/(300 K)
Vf = 700 mL

Answer:

The final volume after heating will be 700 mL.

Question 21

The pressure of a mixture of nitrogen, carbon dioxide, and oxygen is 150 kPa. What is the partial pressure of oxygen if the partial pressures of the nitrogen and carbon dioxide are 100 kPA and 24 kPa, respectively?

Answer 21

P = Pnitrogen + Pcarbon dioxide + Poxygen

150 kPa = 100 kPa + 24 kPa + Poxygen

Poxygen = 150 kPa - 100 kPa - 24 kPa

Poxygen = 26 kPa

Question 22

A cylinder contain a gas of volume 30 L, at a pressure of 110 kPa and a temperature of 420 K. Find the temperature of the gas which has a volume 40 L at a pressure of 120 kPa.

Answer 22

Vi = 30 L, Pi = 110 kPa, Ti = 420 K, Vf = 40 L, Pf = 120 kPa

Final Temperature(Tf) = PfVfTi / PiVi

Tf= (120kPa x 40L x 420K) / (110kPa x 30L)

Tf = 610.91 K

Question 23

A cylinder contain a gas of volume 10 L, at a pressure of 80 kPa and a temperature of 200 K. Find the temperature of the gas which has a volume 20 L at a temperature of 220 K.

Answer 23

Vi = 10 L, Pi = 80 kPa, Ti = 200 K, Vf = 20 L, Tf = 220 kPa

Final Pressure(Pf) = PiViTf / TiVf

Pf= (80 x 10 x 220) / (200 x 20)

Pf = 44 kPa

Question 24

Inversely Proportional

Answer 24

As the value of one variable increases, the value of the other decreases and vice-versa (e.g., pressure and volume)

Question 25

Directly Proportional

Answer 25

As the value of one variable increases, the value of the other increases and vice-versa (e.g., temperature and volume, temperature and pressure)

Question 26

Vapor Pressure

Answer 26

The pressure of the vapor resulting from evaporation of a liquid (or solid) above a sample of the liquid (or solid) in a closed container.

Question 27

Ideal Gas

Answer 27

A gas that behaves exactly as the Kinetic Molecular Theory describes

Question 28

Manometer

Answer 28

Measures the pressure of a gas in a closed container.

Question 29

A balloon contains 30.0 L of helium gas at 103kPa. What is the volume of the helium when the balloon rises to an altitude where the pressure is only 25.0 kPa?

Answer 29

124 L

Question 30

A balloon inflated in a room at 24 c has a volume of 4.00 L. The balloon is then heated to a temperature of 58.0 c . What is the new volume if the pressure remains constant?

Answer 30

4.46 L

Question 31

At 34.0 c the pressure inside a nitrogen filled tennis ball with a volume of 0.148 L is 212 kPa. How many moles of nitrogen gas are in the tennis ball?

Answer 31

0.0122 moles