Thermal physics

Question 1

What is internal energy?

Answer 1

The sum of the randomly distributed kinetic energies and potential energies of the particles in a body.

Question 2

How is the internal energy of a system increased?

Answer 2

When energy is transferred to it by heating or when work is done on it

Question 3

What happens to energy during a change of state?

Answer 3

The potential energies of the particle ensemble are changing but not the kinetic energies.

Question 4

Continuous flow formula for specific heat capacity

Answer 4

c= Q2-Q1/ (m2-m1)Δθ

Question 5

What is Boyle’s Law?

Answer 5

Boyle’s Law states that the volume of a gas is inversely proportional to its pressure when temperature is kept constant.

Question 6

What is Charles’ Law?

Answer 6

Charles’ Law states that the volume of a gas is directly proportional to its absolute temperature when pressure is kept constant.

Question 7

What is the pressure law? (Guy- Lussac’s Law)

Answer 7

Gay-Lussac’s Law states that the pressure of a gas is directly proportional to its absolute temperature when volume is kept constant

Question 8

What is Avogadro’s Law?

Answer 8

Avogadro’s Law states that the volume of a gas is directly proportional to the number of moles of gas when pressure and temperature are kept constant.

Question 9

What is Absolute Zero?

Answer 9

Absolute zero is the temperature at which a substance has minimum internal energy, that is the sum of the kinetic and potential energies of its particles cannot be lowered any further. It is -273.15 degrees celsius

Question 10

Work done equation?

Answer 10

work done= p ΔV

Question 11

Molar Mass formula?

Answer 11

M= mass of substance/ number of moles

Question 12

What is molecular mass?

Answer 12

The sum of the masses of the atoms in a molecule. It is measured in atomic mass units.

Question 13

What is Brownian motion?

Answer 13

Brownian motion​ is the ​random motion of larger particles in a fluid​ caused by ​collisions​ with surrounding particles, and can be observed through looking at smoke particles under a microscope. Brownian motion contributed to the ​evidence for the existence of atoms​ and molecules.

Question 14

Assumptions made in the derivation of the kinetic theory equation (5)

Answer 14

● No intermolecular forces​ act on the molecules
● The ​duration of collisions is negligible​ in comparison to time between collisions
● The motion of molecules in ​random​, and they experience​ ​perfectly elastic collisions
● The motion of the molecules follows ​Newton’s laws
● The molecules ​move in straight lines​ between collisions

Question 15

What is internal energy for an ideal gas?

Answer 15

The sum of the kinetic energies of all the gas molecules, as there are no intermolecular forces, there is no potential energy.

Question 16

How do you derive the kinetic theory model equation?

Answer 16

Consider a cube with side length l, filled with particles of mass m and speed u. Find the force exerted on the wall, by finding the change in momentum and finding the time between collisions.

Question 17

Explain, with reference to molecular motion, why the pressure of a gas increases with temperature

Answer 17

-Average kinetic energy of the molecules increases with temperature
-More collisions occur as they occur more frequently
-Average change in momentum of a particle from collision is greater
-And the rate of change of momentum is greater
- Hence force, and therefore pressure during collision is greater

Question 18

Explain what is meant by a ideal gas

Answer 18

An ideal gas is a gas which follows the gas laws perfectly, meaning that there is no other interaction other than perfectly elastic collisions between the molecules. This means that there are no intermolecular
forces between the molecules