Specific heat capacity GCSE physics lesson: ΔE = m c Δθ and the required practical

Specific heat capacity: the practical's results

Mia found the specific heat capacity of aluminium in the required practical. Use her results: show your working on paper, and give energies in joules.

1. Mia heats a 1.0 kg aluminium block, wrapped in insulation, with a 60 W heater for 10 minutes. How much energy does the heater transfer, in joules?
2. The block starts at 20.5 °C. After the heater goes off, its highest temperature is 58.0 °C. What is its temperature change, in °C?
3. Use c = ΔE ÷ (m Δθ) to find the specific heat capacity Mia measured, in J/kg °C.
4. Aluminium's specific heat capacity is 900 J/kg °C. Why is Mia's value higher?
   1. The block warmed more than it should have, because the insulation trapped extra energy
   2. Some of the energy warmed the room, the heater and the thermometer, so the block warmed less than it should have
   3. The heater gave out less energy than 36 000 J
5. What would bring Mia's value closer to 900 J/kg °C?
   1. Heat the block for longer
   2. Put thicker insulation all round the block
   3. Read the temperature the moment the heater goes off, not the highest one
6. With no energy lost, 36 000 J would warm the 1.0 kg block (c = 900 J/kg °C) by ___ °C. Mia's block warmed by 37.5 °C, ___ than that, because some energy escaped.

Specific heat capacity: practice

Show your working on paper. Use ΔE = m c Δθ; turn grams into kilograms, kJ into joules and minutes into seconds first. Water's specific heat capacity is 4200 J/kg °C. The stretch is optional.

Diagnostic question: choose and explain

1. 500 g of water warms from 20 °C to 30 °C. Water's specific heat capacity is 4200 J/kg °C. How much energy did it take?
   1. 21 000 000 J
   2. 21 000 J
   3. 63 000 J
   4. 42 000 J

Practice questions

1. How much energy does it take to warm 2 kg of water by 5 °C, in joules?
2. Copper's specific heat capacity is 385 J/kg °C. What does that mean?
   1. It takes 385 J to warm any piece of copper by 1 °C
   2. It takes 385 J to warm 1 kg of copper by 1 °C
   3. 1 kg of copper melts at 385 °C
3. A 0.8 kg aluminium block (c = 900 J/kg °C) warms from 15 °C to 40 °C. How much energy does it take, in joules?
4. 200 g of oil (c = 2000 J/kg °C) is given 12 kJ of energy. By how much does its temperature rise, in °C?
5. A 2100 W kettle heats 1.5 kg of water for 2 minutes. If all of its energy goes into the water, by how much does the water's temperature rise, in °C?
6. Why is water good for carrying heat round a central-heating system and in hot-water bottles?
   1. Its small specific heat capacity lets it warm up quickly
   2. Its large specific heat capacity means each kilogram holds a lot of energy for each degree, and cools slowly
   3. It doesn't lose any heat to the room
7. The same energy goes into 1 kg of water (4200 J/kg °C), 1 kg of aluminium (900 J/kg °C) and 1 kg of copper (385 J/kg °C). Which warms up the most?
   1. The water
   2. The aluminium
   3. The copper
   4. All warm up the same
8. In the required practical, Kian forgets to wrap the block in insulation. How will his value of c compare with the true one?
   1. Too high: more heat escapes, so the block warms less
   2. Too low: energy is lost, so c is smaller
   3. The same: insulation only keeps the block safe to touch
9. A 1.5 kg block is heated by a 40 W heater for 5 minutes and warms by 8.0 °C. What is its specific heat capacity, in J/kg °C?
10. A 3 kW heater runs for 7 minutes and warms the water in a tank by 5 °C. If no energy is lost, what is the mass of the water, in kg?
11. Stretch (Higher): Zara plots the temperature of a 0.5 kg block against the energy put in. Her straight line goes from 20 °C at 0 J to 80 °C at 24 000 J. Its gradient is ___ °C per joule, and the block's specific heat capacity is ___ J/kg °C.

Support: Write each quantity on its own line with its unit before any multiplying: m = … kg, c = … J/kg °C, Δθ = end − start = … °C, ΔE = … J. Then put them into ΔE = m c Δθ, or its rearranged form.

Specific heat capacity: exit

Write m, c and Δθ with their units before you put them into the equation.

1. A 0.6 kg block of iron (c = 450 J/kg °C) is heated from 20 °C to 70 °C. How much energy does it take, in joules?
2. A 400 g block takes 7.2 kJ to warm by 20 °C. What is its specific heat capacity, in J/kg °C?

Exit check

Energy from a temperature change, then c from grams and kJ, shows who uses the change and the right units.

A 0.6 kg block of iron (c = 450 J/kg °C) is heated from 20 °C to 70 °C. How much energy does it take?

Specific heat capacity

Show your working. Write each quantity with its unit first, in kilograms, joules and seconds. Water's specific heat capacity is 4200 J/kg °C.