3 - Thermal

Question 1

Why does temperature remain constant when a substance is changing state?

Answer 1

intermolecular bonds are formed during freezing/ broken during boiling
intermolecular bond forming process releases energy
intermolecular potential energy PE decreases and the difference is transferred as heat
average kinetic energy KE of the particles does not decrease
temperature is related to average KE of particles, so temperature remains constant

Question 2

What is the unit for specific latent heat?

Answer 2

J kg-1

Question 3

What is the unit for specific heat capacity?

Answer 3

J kg-1 K-1

Question 4

Why does temperature of an ideal gas decrease when volume increases?

Answer 4

temperature is a measure of the average kinetic energy of the molecules
energy/momentum to the piston is provided by energy/momentum of molecules which collide with it
average kinetic energy decreases

Question 5

What is thermal energy?

Answer 5

net energy transferred between two bodies at different temperatures

Question 6

What is the difference in internal energy between a solid and an ideal gas?

Answer 6

internal energy in solid = KE + PE

internal energy in gas = only KE, so internal energy is total of KE

Question 7

How is an emission spectrum formed?

Answer 7

electron drops from high energy level to low energy level
energy levels are discrete
wavelength and frequency are related to energy change (E=hf)
therefore wavelength is also discrete