Change of State
6 marks · NormalIn an experiment to find the specific heat capacity of a liquid, the following apparatus is set up:
The experiment is performed twice with the same mass of liquid but different power outputs of the heater. The following data is collected:
| Trial | Mass (kg) | ΔT (°C) | Heater Power (W) | Time (s) |
|---|---|---|---|---|
| 1 | 0.5 | 20 | 40 | 400 |
| 2 | 0.5 | 15 | 50 | 300 |
Write down the equation needed to calculate the specific heat capacity of the liquid from the energy supplied and the temperature change.
Calculate the specific heat capacity from the data in Trial 1. Show your working.
Suggest one practical reason why the values obtained in Trials 1 and 2 may not be exactly the same.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
(a) ΔQ = m × c × ΔT or c = Q/(mΔT) · must show correct formula
(b) Q = Power × time = 40 × 400 = 16000 J; c = Q/(mΔT) = 16000/(0.5×20) = 16000/10 = 1600 J/kg°C · must show energy calculation, substitution, final answer with unit
(c) Heat loss to surroundings; not all supplied energy goes into the liquid, or measurement errors like thermometer lag or misreading power or time. · must show heat losses, measurement errors (any one with explanation)
Show mark scheme and worked solution
Marking points
M1 (a) · 1 mark · State correct equation for specific heat capacity.
M2 (b) · 1 mark · Correct calculation of energy supplied (Q = P × t).
M3 (b) · 1 mark · Correct substitution into c = Q/(mΔT).
A1 (b) · 1 mark · Final answer: 1600 J/kg°C, correct to ±30. (follow-through)
M4 (c) · 1 mark · Identifies practical source of error (heat loss or similar).
M5 (c) · 1 mark · Explains why this leads to a difference in measured value.
Worked solution
a) The relevant equation is c = Q / (m x ΔT) or ΔQ = m × c × ΔT.
b) Specific heat capacity = 1600 J/kg°C.
c) In practice, some heat is lost to the surroundings or absorbed by the beaker, or thermometer readings may lag or be misread, making the measured values in each trial slightly different.