6.5 - Ideal Gases Flashcards
What is absolute zero and what is it defined as?
- -273°C (or 0K)
- The temperature at which the molecules in a substance have 0 kinetic energy
Has absolute zero been achieved here?
No, at the moment it is purely theoretical as the amount of work necessary to remove heat from a substance increases the colder you try to go.
Reaching it is purely theoretical.
What are the assumptions of an ideal gas?
The volume of each molecule is considered to be negligible.
What is an ideal gas?
A gas that follows the gas laws perfectly - the only interactions happening in a fixed container of an ideal gas are perfectly elastic collisions of the molecules.
What is Boyle’s law?
P ∝ 1/V
(if temp of ideal gas is constant)
What is the relationship between the pressure and volume for a fixed mass of gas at constant temp? (equation)
P₁V₁ = P₂V₂
initial pressure (Pa) and volume (m³) final pressure and volume
What does Boyle’s law look like as a graph?
Reciprocal function in the positive axis
y = 1/x
What happens to a Boyle’s Law graph if the temperature increases?
The graph becomes further from the origin.
What is Charle’s Law?
V ∝ T
(if the pressure of an ideal gas is constant)
What is the relationship between the volume and temperature for a fixed mass of gas at constant pressure? (equation)
V₁/T₁ = v₂/T₂
initial volume (m³) / initial temp (K) = final volume / final temp
What does Charles’s Law graph look like (in °C)?
Positive straight line with an x intercept at -273°C.
What is the relationship between pressure and temp?
If the volume is constant, P ∝ T.
P₁/T₁ = P₂/T₂
What is an equation that shows the relationships between pressure, volume and temp?
pV ∝ T
What is pressure defined as?
The frequency of collisions of the gas molecules per unit area of a container.
If the temperature of a gas is increased, how does this effect the molecules in a fixed container and what does it conclude (assuming this is an ideal gas)? (long worded question - 5 points)
- The the gas gets hotter, the molecules move faster
- The molecules collide with the surface of the walls more frequently
- Each collision applies a force across the surface area of the walls
- The faster the molecules hit the walls, the greater force on them (F= Δmv)
- Therefore pressure also increases
If the volume of a container with gas decreases and T stays constant, how is pressure effected? (Consider Boyle’s law)
- Smaller surface area = more collisions
= Therefore creating more pressure
What are the 2 ways of writing the ideal gas equation?
pV = nRT
p = pressure
V = volume
n = number of moles (mol)
R = Molar gas constant = 8.31Jkg⁻¹mol⁻¹
or
pV = NkT
N = number of molecules
k = Boltzmann constant = 1.38 x 10⁻²³JK⁻¹
T = temp (K)
What are the 4 rules for a gas to be an ideal gas?
- Collisions which are elastic
- Can’t be liquified
- Has no interactions between the molecules (except during collisions)
- Obeys the ideal gas laws (Boyle’s, Charles’, Pressure Laws)
What is a mole?
A unit used to measure the amount of substance.
( 1 mole = 12g of carbon-12 = 6.02x10²³ atoms)
What is the work done when a volume of gas changes at constant pressure defined as?
W = pΔV
W = work done (J)
p = external pressure
V = volume of gas
What is an example of ‘work done by a volume of gas’?
In a steam engine where expanding steam (the volume of gas) pushes a piston to turn the engine.
What is Avogadro’s Constant and what is it defined as?
6.02 x 10²³
The number of atoms of carbon-12 in 12g of carbon-12.
What is one mole of any element equal to?
The relative atomic mass (in grams).
What is the molar mass?
The mass of a substance in grams, in 1 mole
(unit = g mol⁻¹)
What is the equation to find the number of moles?
Number of moles = mass (g) / molar mass (g mol⁻¹)
What is the Boltzmann constant?
k = R / Na = 1.38 x 10⁻²³ JK⁻¹
R = molar gas constant (8.31)
Na = Avagadro’s constant
Why is the Boltzmann constant so small?
The increase in kinetic energy of a molecule is very small for every incremental increase in temperature.
What is the definition of the Boltzmann Constant?
The relation of the average kinetic energy of gas particles and the temperature of the gas.
What is the difference between molar and molecular mass?
Molar mass - the mass of the mole of a substance (g/mol)
molecular mass - the mass of a single molecule and is expressed in atomic mass units
What does adiabatic mean?
No heat transfer in the system and Energy is only transferred as work done
