Thermal (Modelling Gases)

Question 1

What are the properties of a Gas?

Answer 1

Temperature
* measured in Kelvin (K)

Volume
* measured in cubic meters (m^3)

Number of Particles
*mass (kg) or moles (mol)

Pressure

• the magnitude of the force at the normal per the unit area
• measured in Pascals [Pa = (N)*(m^-2)] Newton per meter squared

Question 2

What is Boyle’s Law?

How does a graph describing the law look like?

Answer 2

Pressure is inversely proportional to the volume
*Constants: mass & temperature

Graph of Pressure over Volume looks like an exponential decay

Question 3

PRACTICE IB QUESTION:

How is Boyle’s law explained with the kinetic model?

Answer 3

Kinetic model = talking about the molecular level (the movement of the particles)

1. When volume decreases, the particles hit the wall more often
2. Therefore, the rate of change of momentum increases
3. Because force is equal to the rate of change of momentum, the force increases
4. Because pressure is force over area, the pressure increases

Question 4

What is Charle’s Law?

How does a graph describing the law look like?

Answer 4

volume is directly proportional to the absolute temperature
*Constants: mass & pressure

Graph of Volume over Temperature is a straight positive slope (with an x-intercept at 0K or -273C)
* Theoretically meaning that at absolute zero, the gas has no volume

Question 5

What is The Third/Last Law?

How does a graph describing the law look like?

Answer 5

pressure is directly proportional to the absolute temperature
*Constants: mass & volume

Graph of Pressure over Temperature is a straight positive slope (with an x-intercept at 0K or -273C)
* Theoretically meaning that at absolute zero, the gas has no pressure

Question 6

When combining the constants from the laws of gases, what can you deduce?

Answer 6

In a closed system:

P1)(V1) (P2)(V2
———— = ————-
T1 T2

Question 7

What is Avogadro’s Law?

Answer 7

number of particles is directly proportional to the volume of the gas

Constants: temperature & pressure

• this means that equal volumes of gas contain the same number of particles (regardless of the size of the particles!)

Question 8

What is Avogadro’s Constant

Answer 8

(Na)

a mol. a measure of quantity (an amount) defined by the number of atoms in 12 grams of carbon-12

Question 9

What is Molar Mass?

Answer 9

the mass of one mol of a substance

* Atomic Mass Units (AMU)

Question 10

How do you calculate the no. of mols with mass?

Answer 10

no. of Mols = total mass / molar mass

• Total mass in grams (g)
• molar mass in AMU

Question 11

What is an Ideal Gas?

Answer 11

a theoretical gas that obeys the gas laws perfectly under all conditions and fit the equations exactly.

Question 12

What is the “Equation of state” / “Ideal gas law”?

Answer 12

pV = nRT

P = pressure (Pa or N m^-2)
V = volume (m^3)
n = quantity of gas (# mols)
T = temperature (K)
R = Gas Constant (8.31 J kg^-1 mol^-1)

Question 13

What assumptions do we make when applying gas laws to real gasses?

Answer 13

1. Newton’s laws of motion applys to the gas particles (atoms & molecules)
2. The gas particles move continuously with a range of speeds
3. The volume of the individual particle is tiny compared to the volume of the gas cloud (there’s a lot of empty space between molecules)
4. The collisions between the particles and the container are perfectly elastic collisions (no Ek lost)
5. There are no intermolecular forces of attraction or repulsion (removes electric & potential energy, we only include kinetic energy)
6. Collisions are considered instantaneous (assume no time spent b/c actual duration of the collision is instantly compared to the time between collisions)

Question 14

What are some properties/limitations of Real gases?

Answer 14

• They behave like ideal gases at room temperature & pressure
• At high temperature and pressure, they interact with each other more and lose their ideal properties
• Real gases also become liquid at a certain point, so they can’t be used in equations beyond their condensing point