Question 2B
(i) Define heat capacity
(ii) An electric kettle rated 1.2 kW is used to heat 800 g of water initially at a temperature of 20 0C. Neglecting heat losses, calculate the time taken for the kettle to heat the water to its boiling point.
[Take boiling point of water = 101 0C, specific heat capacity of water = 4200 J kg-1 K-1].
Observation
Part (b) Candidates’ responded poorly in this part as many candidates were defining specific heat capacity in place of heat capacity.
The expected answers are that candidates should:
- Measure and record in cm3 five values of v
- Measure and record five values of m correctly evaluated to g
- Initial temperature0 measured and recorded in oC
- Measure and record five values of1 in oC and in trend
- Correctly evaluate five values of 1 –o)
- Show composite table containing at least v, m, 1 and
- Plot a graph using reasonable scale
- Draw line of best fit
- Determine the slope of the graph
- Evaluate k =
- State any two of the following precautions
e.g - Avoided splashing of water
- Stirred continuously (for even distribution of heat)
- Avoided parallax error on the thermometer/measuring cylinder
- Repeated readings shown on table
- Ensured the heated mass was gently dropped into the beaker
b(i) Heat Capacity
Is the quantity of heat required to raise the temperature of a substance by 1K or 1oC
(ii) Pt = mc
1200 x t = x 4200 (101 – 20)
t =
= 226.8 secs.