Laboratory work: comparing quantities of heat when water at different temperatures is mixed
Aim: to check that the heat given up by the warmer water, Q₁ = c·m₁(t₁ – t), and received by the cooler water, Q₂ = c·m₂(t – t₂), are approximately equal. Equipment: two 1 l vessels, a thermometer, a measuring cylinder, warm and cold water. Procedure: 1) measure hot water of mass m₁ (1 ml of water ≈ 1 g) with the cylinder, pour it into the first vessel and measure t₁; 2) measure cold water of mass m₂, pour it into the second vessel and measure t₂; 3) pour the cold water onto the hot water, stir and measure t; 4) calculate Q₁ and Q₂; 5) change the masses and repeat three times; 6) record the results in a table. Safety: the hot water must not exceed 60 °C and only the teacher or a senior helper prepares and pours it; do not break the thermometer. The Celsius scale is enough for temperature differences because ΔT = Δt.
Groups enter their results into a shared table and find which group has the smallest difference between Q₁ and Q₂, then discuss why (fast stirring, vessel, air).