Section 1 - Paper 1 - Solids, Liquids and Gases

What is density?

What is density?

Mass per unit volume

How can you find the density of an object?

• Use a balance to measure its mass.

• If it’s a box shape, find the volume by multiplying its length, width, and height with a ruler.

• If it’s an irregular shape, measure the volume by submerging it in a beaker of water and calculating the water’s displacement. Or use a eureka can and find the volume of water displaced as it is poured into a measuring cylinder next to it.

• Use the formula mass/volume to find the object’s density.

What is pressure measured in?

Pascals - the symbol is a normal p

What is absolute zero?

0 kelvins, or -273 ‘C. Where particles have as no energy in their kinetic stores. It is impossible to actually reach due to the amount of work necessary to remove heat from a substance.

What is the temperature (in Kelvins) of a gas proportional to?

The temperature of a gas (in Kelvins) is proportional to the average energy in the KE stores of its particles.

Discuss/Explain particle theory?

• As gas particles move about, they randomly bang into each other and the walls of the container, exerting a force and causing their momentum and direction to change.

• In a sealed container, particles smash against the walls, creating an outward pressure.

• Heating the gas causes the particles to move faster and have more energy in their KE stores. This means they hit the container walls with more force + more frequently, creating more pressure.

• Temperature and pressure are proportional.

• If you put the same amount of gas in a bigger container, the pressure decreases as they will be fewer collisions between the gas particles and the container walls.

• Volume and pressure are inversely proportional.

What is Boyle’s Law?

If temperature remains constant, volume of a gas is inversely proportional to the pressure of the gas”

Discuss pressure when scuba diving

• When scuba diving, the pressure increases around you and in your lungs too - due to the added water weight.

• Therefore, the volume of air in your body decreases, causing your lungs to decrease in volume.

• If you rise to the surface too quickly, without expelling some gas, the pressure of the gas inside your lungs is much greater than atmospheric pressure levels, and your lungs could burst.

Why do planes that fly at high altitudes have to be pressurised?

Because the air pressure decreases at high altitudes, and low air pressure means that humans cannot take in oxygen fast enough for the body’s needs.