Revise: Heat and Thermal Phenomena
Units of heat, internal energy, thermal and specific heat capacity, the law of heat exchange, and change of state with latent heat.
Q = mcΔT; specific heat capacity is a property of the material (per kg).
2 kg of water heated 20°C needs 168,000 J.
Heat lost by the hot object = heat gained by the cold object (insulated system).
0.3 kg water at 80°C + 0.5 kg at 20°C mix to 42.5°C.
Temperature stays constant during a state change — energy breaks/forms bonds, not KE.
Ice water stays at 0°C the whole time the ice is melting.
Q = mLᵥ; vaporization needs far more energy than an equivalent temperature change.
0.5 kg of water to steam needs 1,130,000 J.
Q = mLf; fusion (melting) needs less energy than vaporization for the same substance.
0.8 kg of ice needs 267,200 J to melt.
Heat is energy, measured in joules; 1 cal = 4.186 J.
150 food Calories (kcal) ≈ 628,000 J.
Heat is energy IN TRANSFER; internal energy is what a substance HAS.
Hot coffee transfers heat to the air as it cools, losing internal energy.
C = Q/ΔT; thermal capacity depends on an object's total mass, unlike specific heat capacity.
A larger pot of water has a larger thermal capacity and heats more slowly.
Boiling point rises with pressure; water's melting point is a rare exception (falls with pressure).
A pressure cooker raises boiling point, cooking food faster.