In GCSE Science students will look at the transfer of heat energy. This is the last of eight quizzes on that subject and it looks at specific heat capacity and how it is used to measure how much thermal energy can be absorbed by a material.

When thermal energy (heat) is transferred to an object, its temperature will increase. How much it increases depends on how much thermal energy is transferred, the mass of the object and its specific heat capacity. Specific heat capacity is the amount of energy required to change the temperature of one kilogram of a substance by one degree Celsius. In practical terms, it is a useful measure of how much thermal energy can be absorbed by a material. Those with lower specific heat capacities will absorb less and vice versa. This is particularly useful to heating engineers and householders as it enables them to make informed decisions about what materials to use for things like storage heaters and central heating systems.

Central heating systems exist in different forms but the most common ones use water. In such systems, as hot water passes through the system it gradually transfers its stored thermal energy to the surroundings, heating the different rooms in the house. Since water has a high specific heat capacity by the time it reaches the last rooms there will still be enough of the heat it absorbed left to warm them. A substance with a low specific heat capacity would be cold much sooner.

One system that is very popular is underfloor heating. This is not a new idea - the Romans had underfloor heating over 2,000 years ago (look up 'hypocaust' if you want to know more). The most efficient of this type of system, which uses specific heat capacity to the maximum, is to lay a concrete slab as a base. Plastic water pipes are then laid down across the whole surface of the slab and then buried in what is called a 'screed'. The screed is also usually based on concrete. Concrete has a good specific heat capacity - not as good as water but high enough to make it a good heat storage medium. Warm water is then pumped through the pipes and heats up the concrete, which gradually absorbs the heat energy, releasing it slowly into the room. When the water pump and water heater are switched off, the concrete still has a lot of stored heat that it can release into the room. Because the heat is coming from the whole of the floor, it is a very efficient way of heating a building.

1.

What are the units of specific heat capacity?

J/kg^{o}C

Jkg^{o}C

J^{-1}kg/^{o}C

W/kg/^{o}C

This needs to memorised for the exam

2.

A block of copper was heated from 18^{o}C to 33^{o}C using 35 thousand joules of energy. The specific heat capacity of copper is 385 J/kg^{o}C. What was the mass of the block of copper?

2.6 kg

0.385 kg

385 kg

It can't be worked out without more information

Dividing the energy by the specific heat capacity multiplied by the temperature rise gives the answer

3.

A homeowner uses a wood burning stove to heat his house. The casing of the stove gets hot when the wood inside is burning and is made from 120 kg of cast iron. It took 3,276 kJ of energy to raise the temperature of the stove casing from 18^{o}C to 70^{o}C. What is the specific heat capacity of the cast iron in J/kg^{o}C?

0.525

525

1.904

1,904

This is testing how well you understand units. The calculation using 3,276 kJ will give you the answer in kJ/kg^{o}C but the question asks for the answer expressed in J/kg^{o}C

4.

How much energy must be transferred to raise the temperature of 2 kg of water from 27^{o}C to 40^{o}C? Water has a heat capacity of 4,200 J/kg^{o}C

109,200 kJ

10,920 kJ

1,092 kJ

109.2 kJ

Straighforward use of the specific heat capacity equation. The specific heat capacity is given in joules but the units of the answers are in kilojoules, so you needed to divide your answer by 1,000

5.

What symbol is used to represent the specific heat capacity of a material?

a

b

c

shc

c is also used to represent the speed of light

6.

As well as the specific heat capacity, what else affects the amount of thermal energy a material can store?

Nothing - it's just the specific heat capacity that matters

The temperature change

The mass

Both temperature change and mass

Applying a higher temperature and using more of the material will increase the amount of thermal energy stored (and vice versa of course)

7.

When a particular car engine is working normally, 1.5 kg of coolant at a temperature of 114^{o}C with a specific heat capacity of the of 3,800 J/kg^{o}C passes through the radiator each second. If 91.2 kJ of energy is transferred to the surroundings, what is the temperature of the coolant leaving the radiator?

16^{o}C

98^{o}C

0.016^{o}C

120^{o}C

Four things here - did you pay attention to the units, did you rearrange the equation correctly and did you remember that the answer is the temperature **difference** and that the temperature will go down because a radiator is designed to get rid of heat from a coolant? Well done if you did!

8.

The specific heat capacity of water is 4,200 J/kg^{o}C. The specific heat capacity of mineral oil is 2,100 J/kg^{o}C. Based on this information, which statement is **correct**?

Mineral oil would be of little use for storing heat

Water would be no use for storing heat

Kilogram for kilogram, mineral oil can absorb more thermal energy than water

Water can store more heat than the same mass of mineral oil

You should know from your studies that both water and mineral oil are used for storing heat (oil filled radiators and central heating systems), so the first two statements are incorrect. Water has a greater specific heat capacity than the mineral oil so that rules out the third answer

9.

Substances with a low specific heat capacity can store how much thermal energy?

They can not store any thermal energy

They can store some thermal energy

They can store a lot of themal energy

They can store an unlimited amount of thermal energy

The greater the specific heat capacity, the greater the quantity of thermal energy the material can store

10.

In a laboratory experiment, a group of students used a copper block with a hole drilled in for a thermometer and a second hole in for the heater. Which of the following is **not required** to calculate the specific heat capacity?

Joulemeter reading at the start and end

Time taken

Starting temperature

Mass in kg of the copper block

This question tests if you know that the equation for specific heat capacity is Energy = Mass x Specific heat capacity x Temperature change. There is no mention of time

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