14.1 Gas Laws Flashcards
What happens when car tyres are pumped?
When you pump up car tyres, volume doesn’t change much but pressure rises until rubber walls are taut enough to support the weight.
What’s the Boyle’s Law experiment?
In 1660, Robert Boyle investigated the spring of the air.
- Increasing pressure in the air reservoir forces oil up the callibrated tube. Decreasing pressure allows oil back out.
- A bourdon gauge measures air pressure in the reservoir but a pressure sensor and data logger can be used. A valve allows air to air pump, (circle with X)
- Provided T of trapped air is constant and V is constant in calibrated tube and reservoir, variation in volume with pressure can be investigated.
What is Boyle’s Law?
Pressure is proportional to 1/V, and pV=constant.
If mass is doubled, what effect does this have on pressure? What proportions can be found?
If mass is doubled, this doubles pressure for same volume, so pV is proportional to mass of gas and pressure is proportional to density.
What did Daniel Bernoulli discover?
Daniel Bernoulli discovered in 1738 that a gas is a mixture of small moving molecules which exert pressure by bouncing off the container. A piston, (weight), is supported by gas molecules which exert an upwards force depending on mass, velocity, and number of particles.
What happens to pressure when volume is halved or mass is doubled?
If volume is halved, the wall will be striked twice as often, doubling pressure. The same effect occurs when number of particles, mass, is doubled.
Pressure is proportional to N, number of particles for constant T and volume.
What is a mole? What is the mass of one mole?
A mole : the amount of substance which contains the same number of particles as 12g of carbon-12.
A mass of one mole is the molar mass, ie - for oxygen this is 32g mol^-1.
How do you find N?
N=n *Na
N - number of particles
n - number of moles.
Na - Avocadro constant
When does Boyle’s Law not apply?
Boyles’ law doesn’t apply when real gases are largely compressed as molecules interact, exerting Van der Waals forces on each other leading to condensation. An ideal gas has no interaction and molecules are so tiny they occupy negligible volume. All gases behave ideal at high separation.
Only small molecules like hydrogen and helium behave ideal in these conditions.
What led to the discovery that there is absolute zero temperature?
Jacques Alexander César Charles investigated how volume at constant pressure changes when heated. Volume and T are proportional.
For every degree rise in temperature, volume increases by 3.66*10^-3 * volume at 0 degrees celsius. If V is constant, the same pattern is shown for pressure.
The graphs have to be extrapolated to find absolute zero where movement of molecules stops altogether.
Volume at 0 degrees celsius is 1 m^3.
By converting degrees into kelvin, a graph can be drawn where no extrapolation is needed.
What is absolute zero?
-273 degrees celsius.
What is the melting point & boiling point of water?
273 and 373 K
What’s the experiment to find absolute zero?
Use a glass filled capillary tube. Air filled space is cylindrical in shape, and length L changes at different temperatures, indicating the change in volume. The tube has a liquid index, mercury, and a seal at the bottom. If the tube is mounted in a beaker of water, the temperature can be measured over a range, alongside the volume. Ensure that recorded temperature of water is close to air temperature inside capillary tube.
What is the ideal gas law?
pV=NkT, where N is number of molecules and k is Boltzmann’s constant.
pV=nRT using the gas constant, 8.31 J mol^-1K^-1
How does oxygen behave at high and low temperatures?
Gases like oxygen approximate well to ideal gases at room temperature and atmospheric pressure but at low temperature molecules come close enough to interact. At 90K, the gas condenses into a liquid, and pressure falls beyond the rate that temperature does as oxygen cools below its boiling point.
