Paper 2 Thermal Physics Route Answers

Q1 Choosing the correct model

1. Latent heat for melting and specific heat capacity for warming water. [2]
2. Supplied energy changes particle arrangement/separation during melting rather than increasing average kinetic energy. [2]
3. $E=m{L}_f+mc\Delta T$ for water from $0^{\circ }\mathrm{C}$ to $20^{\circ }\mathrm{C}$. [2]

Q2 Gas and temperature

1. Gas laws use thermodynamic temperature. [1]
2. $T_1=293\mathrm{K}$, $T_2=353\mathrm{K}$, so $p_2/p_1=T_2/T_1=1.20$. [2]
3. Higher temperature means greater mean molecular kinetic energy; molecules collide with walls more frequently/with larger momentum change, increasing pressure at fixed volume. [3]

Q3 First-law classification

1. Approximately adiabatic. [1]
2. Work done on the gas is positive energy transfer to the gas under the ‘work on gas’ convention. [2]
3. With little heating, work increases internal energy; for an ideal gas this raises temperature. [2]