Year 9 Science · Unit 3 · Lesson 9
Challenge Worksheet
Learning Goals
1. Explain the difference between specific heat capacity and heat capacity.
| Material | c (J/kg·°C) |
|---|---|
| Water | 4,200 |
| Ethanol | 2,400 |
| Aluminium | 900 |
| Copper | 390 |
| Lead | 130 |
Source: values used in Lesson 9.
2. (a) A 0.2 kg lead fishing sinker warms by 15 °C in an angler’s hand. Calculate the energy it takes in. (b) Equal masses of ethanol and water take in the same amount of energy. Using Table 1, which one warms more, and by what factor?
(a) Energy J
(b) Warms more, by a factor of
Find the error: three calculations
(a) Heat 0.25 kg of water from 20 °C to 100 °C. Q = 0.25 × 4,200 × 100 = 105,000 J
(b) Heat a 500 g copper pan by 30 °C. Q = 500 × 390 × 30 = 5,850,000 J
(c) A 2 kg iron block (c = 450 J/kg·°C) takes in 18,000 J. ΔT = 18,000 × 2 × 450 = 16,200,000 °C
3. Each calculation has one error. Say what went wrong, and write the correct answer with its unit.
| Part | What went wrong | Correct answer |
|---|---|---|
| (a) | ||
| (b) | ||
| (c) |
Investigation: measuring the specific heat capacity of aluminium
A class put an electric heater into a hole in a 1.0 kg aluminium block. A joulemeter measured the energy supplied, and a thermometer in a second hole measured the block’s temperature. The block was not insulated.
| Energy supplied (kJ) | Temperature (°C) |
|---|---|
| 0 | 21.0 |
| 6 | 27.2 |
| 12 | 33.0 |
| 18 | 38.8 |
| 24 | 44.4 |
Source: sample class results.
4. Use the first and last rows of Table 2 to calculate the specific heat capacity of aluminium. Round to 3 significant figures. By what percentage is it higher than the value in Table 1?
c of aluminium J/kg·°C
Higher by %
5. Explain why the class’s value is higher than the true value, and suggest one change to the method that would bring it closer.
Someone claims
“Water’s high specific heat capacity is just a coincidence that life happened to use. If water had a low specific heat capacity, living things would cope easily, and Earth’s climate would be about the same.”
6. Evaluate this claim. Include at least one piece of evidence about climate, one about living things, and one calculation: compare the temperature rise of 1 kg of water and 1 kg of sand (c = 800 J/kg·°C) that each take in 84,000 J.
Water °C
Sand °C