ΔE = mcΔq = 2 kg × 4200 J/kg°C × (80 °C – 20 °C) = 504 000 J = 504 kJ
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How much energy is needed to heat 1 kg of copper by 20 °C?
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How much energy is given out when the temperature of 2 kg of steel falls by 30 °C?
Water has a very high specific heat capacity. This means it can absorb a large amount of thermal energy from a hot object for a given temperature change of the water. Water is used to cool many car engines. The thermal energy store in the engine decreases and the thermal energy store in the water increases. Energy is then transferred from the thermal energy store in the water to the store in the air surrounding the radiator. Water can also release a lot of energy without a large temperature decrease. This makes it a very useful way of transferring large amounts of thermal energy around a house in a central heating system.
Figure 1.13 Water is used to cool many car engines
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Explain why a hot-water bottle is so effective at warming a bed.
DID YOU KNOW?
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What is meant by specific heat capacity?
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How much energy is needed to raise the temperature of 3 kg of steel by 15 °C?
Several tonnes of liquid sodium metal are used as a coolant in some types of nuclear reactor. The liquid sodium transfers thermal energy from the reactor core to water, which then turns to steam and drives the generators.
More about specific heat capacity Example: 0.5 kg of copper at 90 °C is added to 2 kg of water at 10 °C. Calculate the final temperature of the copper and water (T). Assume that the decrease in thermal energy store of the copper = increase in thermal energy store of the water. Change in thermal energy store of copper = 0.5 kg × 380 J/kg°C × (90 °C – T) Change in thermal energy store of water
= 2 kg × 4200 J/kg°C × (T – 10 °C)
190 × (90 – T) = 8400 × (T – 10) (8400 + 190)T = 17 100 + 84 000 T = 101 100/8590 T = 11.8 °C 7
A night storage heater contains 50 kg of concrete. The concrete is heated during the night when electricity is cheaper, gradually emitting stored energy during the day. How much thermal energy is required to warm the concrete from 10 °C to 30 °C? Suggest why concrete is chosen.
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A 1 kg steel block at 80 °C is added to 0.5 kg of water at 10 °C. Calculate the final temperature of the block and the water. Google search: 'specific heat capacity'
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