Gas Laws Flashcards

GASES

• Gases are compressible, meaning their volume can be reduced under pressure.

AIR DUSTER

• When using an air duster, observe what happens after pressing the trigger.

• Consider what could lead to the observed effects.

BELL RINGER

• What distinguishes a gas from a solid or liquid?

• What is air composed of?

FACTORS AFFECTING GAS PRESSURE

• Amount of gas: More gas particles lead to more collisions.

• Volume: Changing the volume affects collision frequency.

• Temperature: Influences the frequency of particle collisions.

GASES

• Increasing the amount of gas increases collisions with the container walls.

• Increased collisions result in increased pressure.

• Pressure is defined as force per square meter (N/m²).

VOLUME

• Changing the volume affects the frequency of collisions.

TEMPERATURE

• Temperature changes the number of particle collisions with container walls.

• Related to kinetic theory.

KINETIC MOLECULAR THEORY

• Gas particles are small, hard spheres with insignificant volume.

• Gas particles are in constant motion.

• Collisions between gas particles are perfectly elastic.

GAS LAWS

\\ween factors affecting gases.

BOYLE'S LAW

• At constant temperature, as pressure increases, volume decreases (and vice versa).

• $P<em>1V</em>1 = P<em>2V</em>2$

• High pressure corresponds to low volume.

• Low pressure corresponds to high volume.

BOYLE'S LAW PROBLEM

• A balloon contains 30.0 L of Helium gas at 103 kPa. What is the volume of the Helium when the balloon rises to an altitude where the pressure is only 25.0 kPa? (Assume constant temperature)

• Answer: 124 L

CHARLES'S LAW

• At constant pressure, as temperature increases, volume increases.

• Convert all temperatures to Kelvin.

• $\frac{V<em>1}{T</em>1} = \frac{V<em>2}{T</em>2}$

CHARLES'S LAW PROBLEM

• 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°C. What is the new volume if the pressure remains constant?

• Answer: 4.46 L

GAY-LUSSAC'S LAW

• At constant volume, as temperature increases, pressure increases.

• $\frac{P<em>1}{T</em>1} = \frac{P<em>2}{T</em>2}$

GAY-LUSSAC’S LAW PROBLEM 1

• The gas in an aerosol can is at a pressure of 103 kPa at 25°C. If the can is thrown onto a fire, what will the pressure be when the temperature reaches 928°C?

• Answer: 415 kPa

GAY-LUSSAC’S LAW PROBLEM 2

• The gas in an aerosol can is at a pressure of 103 kPa at 25°C. The can is put into a freezer and the pressure drops to 59 kPa. What is the temperature of the can inside the freezer?

• Answer: -102.5 °C

QUIZ

• A series of gas law problems are presented, requiring the calculation of unknown variables (V1, T2, V2) using given initial and final conditions for various gases (H2, Kr, SF6, AsH3, NO2, F2).

BELL RINGER

• Review the three previously discussed gas laws and their equations.

• Consider how to mathematically combine them into one law.

AVOGADRO'S LAW

• At constant pressure and temperature, as the number of moles increases, the volume increases.

• Example: 1 mole is 22.4 L, 2 moles is 44.8 L.

COMBINED GAS LAW

• The combined gas law is used when the amount of gas is constant.

• It combines Boyle’s, Charles’s, and Gay-Lussac’s laws.

• $\frac{P<em>1V</em>1}{T<em>1} = \frac{P</em>2V<em>2}{T</em>2}$

COMBINED GAS LAW PROBLEM

• The volume of a gas-filled balloon is 30.0 L at 313 K and 153 kPa pressure. What would the volume be at STP?

• Answer: 39.5 L

BELL RINGER

• List the five gas law equations covered so far.

• Identify other units for pressure besides kPa.

• The volume of a gas-filled balloon is 320.0 L at 305 K and 122 kPa pressure. What would the temperature be of the balloon if the volume increases to 400.0L and the pressure decreases to 57.2 kPa?

• Answer: 178.8 K

IDEAL GAS LAW

• A combination of all the gas laws, with the second set of values at STP (Standard Temperature and Pressure).

• To compare a gas at one condition to STP:

• $\frac{P<em>1V</em>1}{n<em>1T</em>1} = \frac{P<em>2V</em>2}{n<em>2T</em>2}$

• Using standard temperature and pressure with one mole results in a constant value, R.

• R = 8.314 (L•kPa)/(K•mol)

• R = 0.0821 (L•atm)/(K•mol)
  *Rearranging the Ideal Gas Law Equation
  $\frac{PV}{nT} = R$
  $PV = nRT$

• Ideal gas law equation: $PV = nRT$

• R values depend on the units used for pressure.

IDEAL GAS LAW PROBLEM

• A deep underground cavern contains 2.24 x 10^6 L of methane gas at a pressure of 1500 kPa and a temperature of 315 K. How many kilograms of methane does the cavern contain?

• Answer: 2.05 x 10^4 kg of methane

BELL RINGER

• What is an ideal gas?

• What is Dalton’s law of partial pressures?

• What is diffusion? (Draw a picture)

• What is effusion? (Draw a picture)

IDEAL GASES VS REAL GASES

• Ideal gases:

  • Have no volume (insignificant amount).

  • Have neither adhesive nor cohesive properties.

• Real gases:

  • Have volume.

  • Have attractions to other molecules.

  • Real gases typically differ the most from ideal gases when at low temperatures and high pressures.

GAS MIXTURES

• Gases can exist in mixtures, like the air we breathe.

• Each gas in the mixture has its own partial pressure.

• Dalton’s Law of Partial Pressures: $P<em>{total} = P</em>1 + P<em>2 + P</em>3 + … + P_n$

GAS MIXTURE PROBLEM

• A mixture of gas has a total pressure of 183 kPa. The mixture consists of different gases at different pressures. There are 2.5 kPa of oxygen, 45.3 kPa nitrogen, and the rest of the pressure is due to carbon dioxide. What is the pressure of the carbon dioxide?

• Answer: 135.2 kPa

ALL EQUATIONS

1. Boyle's Law: $P<em>1V</em>1 = P<em>2V</em>2$

2. Charles's Law: $\frac{V<em>1}{T</em>1} = \frac{V<em>2}{T</em>2}$

3. Gay-Lussac's Law: $\frac{P<em>1}{T</em>1} = \frac{P<em>2}{T</em>2}$

4. Combined Gas Law: $\frac{P<em>1V</em>1}{T<em>1} = \frac{P</em>2V<em>2}{T</em>2}$

5. Ideal Gas Law: $PV = nRT$

6. Dalton's Law: $P<em>{total} = P</em>1 + P<em>2 + P</em>3 + ….P_n$

DIFFUSION

• The tendency for molecules to move toward lower concentration until the concentration is uniform.

EFFUSION

• Gas escapes through a tiny hole.

DIFFUSION AND EFFUSION

• Gases of lower molar mass diffuse and effuse faster than gases of higher molar mass.

QUESTION

• A container filled with methane gas has a pressure of 200.6 kPa, a volume of 520 L, and a temperature of 500 °C. How many moles of methane gas are present in this particular container? What is the volume of water produced, in mL, if the container got punctured and the methane gas were to auto ignite, assuming a complete reaction and STP? Show all work. Box your answer.

QUICK ACTIVITY

• Heat a small amount of water in a can and then invert the can quickly into room temperature water.

• Hypothesis: Predict what will happen.

• Procedure: Heat can till steam starts to come out of the mouth of the can. Using tongs quickly invert the can into the water bath.

• Explanation: What happened? How do we explain this mathematically? (What laws?)

QUIZ AND INFO.

• Take the first 15 minutes of class to study for the quiz.

• The test has been moved up one day.

REVIEW

• Make sure to look at how the laws relate to one another.

• Think about the variables.

• KMT (Kinetic Molecular Theory).

• Diffusion vs. Effusion.

• Partial Pressures.

• Gas stoichiometry.

REVIEW OF KINETIC MOLECULAR THEORY

1. Gas particles are tiny compared to the space in between them (compressibility).

2. Collisions between molecules are elastic.

3. Gas particles are in constant random motion.

REVIEW QUESTIONS

• The number of times the molecules hit the wall of a container is known as what?

• What all can you do to increase the number of times the molecules hit the wall of a container?

KINETIC ENERGY ORDERING

• Organize pictures from lowest to highest based on the kinetic energy involved (pictures not provided here).

TEMPERATURE CONVERSION

• Convert 25°C to Kelvin.

• Is there a point at which all motion stops? If so, what is the temperature in which that occurs in Kelvin?

REARRANGING THE COMBINED GAS LAW

• Rearrange the combined gas law to find each of the following variables:

  • V1, V2, T1, T2, P1, P2

GRAPHING RELATIONSHIPS

• Graph the information in the table (table data not provided here):

  • Pressure (kPa) vs. Volume (L)

• Graph the information in the table (table data not provided here):

  • Pressure (kPa) vs. Temperature (°C)

PREP FOR QUIZ

• Quiz on various topics of gas laws.

Sample Quiz Questions:

• What is effusion?

• What is diffusion?

• What is the combined gas law formula?

• If the volume of gas increases and the temperature remains the same, what will happen to the pressure?

• If the pressure of a gas increases and the volume stays the same, what happens to the temperature?

• If the temperature of a gas decreases and the pressure remains constant, what happens to the volume?

• The gas in an aerosol can is at a pressure of 103 kPa at 25°C. If the can is thrown onto a fire, what will the pressure be when the temperature reaches 928°C?

• A balloon contains 30.0 L of Helium gas at 103 kPa. What is the volume of the Helium when the balloon rises to an altitude where the pressure is only 25.0 kPa? (Assume constant temperature)

POE (Predict, Observe, Explain)

• Predict what will happen and why.

• Observe what we see.

• Try to explain what is going on.

• Revise our original explanations.

EGG IN BOTTLE DEMONSTRATION

• Predict: Does the air (atmosphere) exert pressure? What is air made of? What is keeping the egg from falling inside the bottle?

• Observe: Draw and annotate what you see.

• Explain: Why does the egg fall into the bottle? Draw what you think allowed the egg to fall into the bottle. How do we get the egg out?

• Food for Thought: What factors (temperature, volume, moles, pressure) changed to allow the egg to fall in? The heat caused the air molecules inside to gain energy and actually even push past the egg. Once the molecules inside were cooled, a vacuum was created. The atmospheric pressure is now greater than the pressure inside the flask, so therefore the egg falls (or is pushed in).

• Re-Explain: Why did the egg fall into the bottle? Why did blowing air in the bottle get it to come back out? What gas laws were at play in this demonstration?

CAN IN WATER DEMONSTRATION

• POE: What will happen if you heat a soda can then flip the can over while submerging it in water?

• Observe: What happened to the can?

• Explain: Explain using the gas laws. What was held constant?

• Re-Explain: Re-explain using your own words.

CARTESIAN DIVER

• Squeeze the bottle.

• Observe what happens.

• Explain why it happens.