Thermal physics

How do you convert from Celsius to Kelvin

Add 273

Why is the absolute scale used?

It doesn’t depend on the properties of a given substance. 0K (absolute zero) means that the particles have minimum internal energy.

Describe the arrangement and energy of particles in a solid, a liquid and a gas.

Solid- regular arranged, vibrate around fixed positions

Liquid- close together, constantly moving past eachother

Gas- spaced very far apart, free to move in all directions

How does Brownian motion give evidence for the particle model of matter

Smoke particles suspended in air can be seen to move randomly in all directions. This must be as a result of random collisions with particles making up the air

What is internal energy?

The sum of the potential and kinetic energies of a system

True or false: At a given temperature, all particles in a material have the same kinetic energy

False. The kinetic energies will be randomly distributed around a central ‘most likely’ amount

How can you increase the thermal energy of a system

We can increase it by heating it up or doing work on the object

Explain the energy changes that occur during a change of state

During change of state the potential energy of the particles change but the kinetic energies don’t change

What equation can be used to determine the energy required to change the temperature of a substance?

E=mc x temp change

What is the specific heat capacity of a substance?

The energy required to raise the temperature of 1kg of a substance by 1K

Give the equation to work of the energy for change of state?

E=mL

What is the specific latent heat of a substance?

The energy required to change the state per unit mass of a substance, while keeping the temperature constant

In an experiment to find ‘c’ for water, lots of energy input escapes to the surroundings. Will this lead to an over or underestimate of specific heat capacity?

An overestimate. The specific heat capacity is calculated as c=E/m x temp change. The energy input will be used but the temperature change of the water will be lower than it should be due to the escaped energy. Therefore c will be too high

What is avogadros constant

The number of atoms there are in one mole of a substance

What are the key assumptions in the kinetic theory of gases?

There are a large number of molecules in random linear motion. Particles are negligibly small compared to the total volume of the gas. All collisions are perfectly elastic. The time taken for a collision is negligibly small compared with the time between collisions. Between collisions there are no forces between particles

Why do gases exert a pressure on the container they’re in?

Gas particles collide with the surfaces of the container. The container exerts a force on the particles to change their direction. The particles exert an equal and opposite force on the container. Pressure is the force applied (by all particles) per unit area.

What is an ideal gas?

A gas where the molecules don’t interact with eachother and the molecules are thought to be perfect spheres

What is the ideal gas equation?

pV=nRT n = number of moles

What is Boyles law?

Pressure is inversely proportional to volume, providing temperature is constant so pV = constant

Assuming constant volume, how are the pressure and temperature of a gas related?

They’re directly proportional so P/T = constant

Use the kinetic theory of gases to explain why a temperature increase leads to a increase in pressure

A temperature increase means the particles have more kinetic energy. More kinetic energy means a greater change in momentum during collisions with the container. There are also more frequent collisions. Change in momentum is proportional to force applied, and therefore to pressure as well.

What is meant by the root mean square speed?

The square root of the mean of the squares of the speeds of the molecules

What does the area under a Maxwell-Boltzmann curve represent?

The total number of particles

How does the maxwell-Boltzmann curve change if the temperature of a gas is increased?

The average particle speed, and maximum particle speed both increase (curve shifts right). The curve becomes lower and more spread out.

What are the units of the Boltzmann coefficient?

J/K

The average kinetic energy of a particle in an ideal gas is equal to what?

1.5kT

True or false: the internal energy in an ideal gas is proportional to absolute temperature

True: In an ideal gas there is no ‘potential energy’ component in the internal energy. This means the internal energy is proportional to the kinetic energy (which is dependent on temperature)