Molecules and Ideal Gases Flashcards
what is the motion of molecules in a gas?
move quickly in any direction (random)
what did Brownian motion note about particles in a fluid?
particles in fluids move around continualy and bump into each other
collisions cause the particles to change direction and speed
what is absolute zero (give a value)?
0 Kelvin
(equivalent to -273oC)
what is the temperature below which it is not possible to cool a gas further?
absolute zero
what is kelvin temperature?
kelvin temperature is proportional to the average kinetic energy of its molecules
why is 0 Kelvin describes as absolute zero?
because the pressure of a gas is 0 when cooled to 0K
it cannot become less than this
what is the Celcius equivalent to absolute zero (0K)
-273oC
how do you work out the temperature in Kelvin given the Celcius temperature?
temperature in Kelvin = temperature in Celcius + 273
how do you work out the temperature in Celcius given the Kelvin temperature?
temperature in Celcius = temperature in Kelvin - 273
work out the Kelvin if Celcius = 0
273K
work out the Kelvin if Celcius = 100
373K
work out the Kelvin if Celcius = 39
312K
work out the Kelvin if Celcius = -200
73
work out the Kelvin if Celcius = -273
0K
work out the Celcius if Kelvin = 0
-273oC
work out the Celcius if Kelvin = 100
-173oC
work out the Celcius if Kelvin = 373
100oC
work out the Celcius if Kelvin = 300
27oC
work out the Celcius if Kelvin = 73
-200oC
A gas in a solid container is at room temperature (300K). The temperature is then raised to 600K. How does the change in temperature affect the volume of the gas?
the volume becomes larger as the particles move more so there is more space between them
A gas in a solid container is at room temperature (300K). The temperature is then raised to 600K. How does the change in temperature affect the pressure of the gas?
the pressure would get higher as the particles would collide more often
A gas in a solid container is at room temperature (300K). The temperature is then raised to 600K. How does the change in temperature affect the temperature of the gas?
the temperature would get higher
it would double (300K to 600K)
A gas in a solid container is at room temperature (300K). The temperature is then raised to 600K. How does the change in temperature affect the speed of the molecules of the gas?
the speed of the molecules would increase as the particles have more kinetic energy (converted from thermal energy)
define the pressure law
for a fixed mass of gas at a constant volume, temperature (measured in Kelvin) is directly proportional to pressure
P ∝ Temperature (Kelvin)
or P = constant x T
P/T = constant
draw a diagram for the apparatus used in an investigation about pressure law
what apparatus is used to investigate the pressure law?
iced water
pressure sensor
data logger
temperature sensor
computer
electric heater
round bottom flask
‘ideal’ gas (air)
note: the combination of a heater and a container of water is known as a ‘heat bath’
what is a water bath?
the combination of a heater and a container of water
the pressure of a gas is …
the pressure of a gas is proportional to its Kelvin temperature
what is the pressure law equation?
if V1 = V2 (constant) then P1 ÷ T1 = P2 ÷ T2
V = volume
P = pressure (Pa)
T = Kelvin
A gas is trapped inside a container with a fixed size (its volume cannot change). What will happen to the gas and pressure if it is heated?
the particles will gain kinetic energy which will make them move faster
this means they will collide with each other and the walls more frequently per second
this causes the force on the walls of the container to increase and so the pressure increases
rearrange the pressure equation P1 ÷ T1 = P2 ÷ T2 so P2 is the subject
P2 = P1 x (T2 ÷ T1)
A car tyre contains air at 1.25 × 105 Pa when at a temperature of 27°C. Once the car has been running for a while the temperature of the air in the tyre rises to 42°C. If the volume of the tyre does not change what is the new pressure of the air in the tyre?
First convert the temperatures into kelvin: T1 = 27 + 273 = 300K, T2 = 42 + 273 = 315K
Now calculate the new pressure: P1 ÷ T1 = P2 ÷ T2 so P2 = P1 x (T2 ÷ T1)
P2 = 1.25 x 105 x (315 ÷ 300)
P2 = 131250 Pa = new pressure of the air in the tyre
what happens to the particles in a gas when the temperature is decreased?
the gas particles move more slowly and the collisions are less hard and less frequent
this means that the pressure also decreases
P1 = 100kPa
T1 = 20oC
T2 = 50oC
Calculate P2
First convert the temperatures into kelvin: T1 = 20 + 273 = 293, T2 = 50 + 273 = 323K
Now calculate the new pressure: P1 ÷ T1 = P2 ÷ T2 so P2 = P1 x (T2 ÷ T1)
P2 = 100kPa x (323 ÷ 293)
P2 = 110.24kPa (2 d.p)
Explain how the motion of particles exert a pressure on the walls of a container referring to force and collisions
the particles in a gas move quickly in all directions and collide with each other and the walls of their container
when gas particles hit the walls of their container they exert a tiny force
the more collisions per second the greater the exerted force and thus a greater pressure
define Boyle’s Law
for a fixed mass of gas at a constant temperature, pressure is inveresly proportional to volume
p ∝ 1 ÷ V
p ∝ constant ÷ V
rearrange p ∝ constant ÷ V to make constant the subject
constant = pV
if the volume is 0.02m3 and the pressure is 5.0 x 105Pa, calculate the constant
p ∝ constant ÷ V
constant = pV
= 5.0 x 105 x 0.02
= 10,000 Pa/m3
given that the constant is 10,000 and the volume is 0.06m3, calculate the pressure
p ∝ constant ÷ V
pressure = 10,000 ÷ 0.06
= 16666.7 Pa
given that the constant is 10,000 and the pressure is 1.2 x 105 Pa, calculate the volume
p ∝ constant ÷ V
V = constant ÷ p
= 10,000 ÷ 120,000
= 0.083m3
draw a graph for Boyle’s law (P/V)
pressure is inversely proportional to volume
draw a graph for Boyle’s law (P/ 1÷V)
pressure is inversely proportional to volume
(inverse is on x-axis so line is directly proportional - straight line through the origin)
what is the equation for Boyle’s law?
when T1 = T2 then P1V1 = P2V2
T = temperature
P = pressure
V = volume
A sealed syringe contains 10 x10-6 m3 of air at 1 × 105 Pa. The plunger is pushed until the volume of trapped air is 4 x 10-6 m3. If there is no change in temperature what is the new pressure of the gas?
P1 = 1 × 105 Pa
V1 = 10 x10-6 m3
V2 = 4 x 10-6 m3
P1V1 = P2V2
P2 = P1V1 ÷ V2
= (1 × 105 x 10 x10-6) ÷ 4 x 10-6 m3
= 2.5 × 105 Pa
rearrange P1V1 = P2V2 to make P2 the subject
P2 = P1V1 ÷ V2
describe the relationship between pressure and temperature for a fixed mass of gas at a constant volume
pressure law
the pressure of the gas is directly proportional to the Kelvin temperature of the gas
is it safer to leave scuba tanks in the hot sun or in water? why?
it is safer in the water
left in the hot sun, the tanks will get ot and the pressure will increase because the gas expands - the tanks could explode
left in the water, tanks are cooler because water has a high heat capacity - the tanks are safe
explain using a gas law what you would expect to happen to a bubble released by a SCUBA diver as it rises to the surface
you may assume that the temperature of the gas does not change
because the mass and temperature are constant, the pressure will decrease because as the bubble rises, pressure decreases
therefore, the volume will increase because Boyle’s law states that pressure and volume are inversely proportional for a fixed mass of gas at a constant temperature
What is Brownian motion?
particles move in zigzap, random motion
this type of movement of any particles in a suspension is known as Brownina motion
large, heavy particles (e.g. smoke) can be mved by Brownian motion by smaller, lighter particles (e.g. air) travelling at high speeds - which is why smoke particles in air appear to move around randomly when you observe them in the lab
What is Kelvin temperature proportional to?
Kelvin temperature is proprotional to the average kinetic energy of the molecule of gas
