Changes of State (OCR Gateway GCSE Physics)

The table shows the specific heat capacities of different materials.

A scientist heats an unknown substance from a solid to a liquid.

The graph shows how the temperature of the substance varies with time.

The scientist has 2.5 kg of the substance and records that it takes 462 kJ of energy to increase it from the lowest to the highest temperature in the liquid state.

Use the graph to calculate the specific heat capacity of the substance.

Suggest what material it could be from the table.

Specific heat capacity = .................................................. J/kg °C

Material = ..............................................................

Suggest two reasons why the scientist cannot be certain that the substance has been identified correctly.

1 ...............................................................................................

2 ...............................................................................................

Two students design an experiment to find the specific latent heat of water.

They set up their equipment as shown in the diagram.
The students also have access to a power supply, a voltmeter, an ammeter, a stop-clock and a top-pan balance. 

Explain how the students could use this equipment to determine an accurate value for the specific latent heat of water.

The students find that 250 g of ice takes 95 kJ of energy to change state.

Calculate the specific latent heat.

Answer = ......................... J/kg

A student puts an ice cube into a beaker. The mass of the ice cube is 40 g.

The ice cube melts.

Mass = .................................... g [1]

 [2]

Describe one difference between a physical change and a chemical change.

A student does an experiment to find the difference between the specific heat capacities of seawater and tap water.

The student places a heater and a thermometer into two beakers, A and B.

Look at the diagram.

Step 2 – ........................................................................................................

Step 3 – ........................................................................................................

Step 4 – ........................................................................................................

Step 5 – Calculate the temperature change of beaker A and beaker B.

[3]

 [1]

1 ..................................................................................................................

2 ..................................................................................................................

[2]

A student has two radiators in her home. They are filled with different liquids and have different power ratings.

Fig. 19.1 shows information about the two heaters.

Fig. 19.1

Table 19.1 shows information about oil and water.

Table 19.1

The student’s conservatory can be very cold.
Sometimes the temperature can get as low as –6 °C.

She thinks that it may be better to use the oil radiator in the conservatory than the water radiator.

Suggest why.
Use the information in Table 19.1 to help you answer.

Both radiators have a ‘cut-out’ which prevents them getting hotter than 60 °C.

Suggest why.

The student knows that the oil heater produces 800 J of energy each second.

Calculate the energy produced by the oil heater in 10 minutes.

Answer = ............................. J

The student wants the oil heater to heat up by 40°C.

Answer = ........................... J [2]

[2]

A student does an experiment to find the specific heat capacity of a metal block.

The diagram shows the apparatus used.

[3]

[2]

The specific heat capacity obtained from the experiment is much larger than expected.

• Suggest two reasons for this difference.
• Suggest two improvements to the method that might give a more accurate value for the specific heat capacity.

A student has two radiators in her home. They are filled with different liquids and have different power ratings. 

The diagram shows information about the two heaters.

The radiators are turned on and both radiators increase in temperature by 40 °C in 1680 seconds.

Show, by calculation, that the heaters take the same time to heat up.

The student has two fires in her home (X and Y) shown in the diagrams below.

Why does fire Y help to save money on the energy bills for her home?

Use calculations of efficiency in your answer.

A student does an experiment using 0.2 kg of water.

Here is some information from the experiment:

Describe how the student should carry out the experiment, including the equipment used.

In your answer calculate the change in internal energy for the water.

You may include a diagram in your answer.