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- Demonstrate understanding of the term thermal capacity.
Thermal capacity is the amount of energy required to raise the temperature of a substance by 1K or 1oC. Note that a change in temperature of 1oC is equal to a change of 1K because their graduations are equal.
Different substances will have different thermal capacities, and different masses of the same kind of substance will also have different thermal capacities.
Heat capacity is another name for thermal capacity.
The formula for thermal capacity is:
- Describe an experiment to measure the specific heat capacity of a substance.
Before we start, the formula for specific heat capacity is:
Measuring the specific heat capacity of a liquid:
Put a known mass of liquid in a beaker, add a thermometer, and insert a heating coil which is connected in series with an ammeter and has a voltmeter across it. Remember that you can calculate the mass of the liquid in the beaker by subtracting the mass of the empty beaker from the mass of the beaker with liquid in it. Ensure that the liquid won’t react with anything else in the system, as this can affect the temperature change.
Your experimental results become more accurate if the beaker is insulated because less heat will be lost from the beaker to the surroundings.
Record the initial temperature of the liquid.
Turn on the heater and start a stopwatch at the same time. Let the temperature of the liquid rise a reasonable amount – at least 10oC should be good – but don’t let it reach boiling point.
Stop the watch and record the time, the final temperature, the reading on the ammeter and the reading on the voltmeter.
You can calculate the energy transferred to the liquid using the equation Q=IVt, where Q is energy transferred in joules (J), I is the current through the heater in amperes (A), V is the potential difference across the heater in volts (V) and t is the time it takes for the temperature change to occur in seconds (s).
Calculate the temperature by subtracting the initial temperature from the final temperature.
You now have the energy transferred (Q), the mass of the liquid (m) and the change in temperature (ΔT). Substitute these values into the equation given above, and calculate the specific heat capacity (c) of the liquid.
It is useful to remember that the specific heat capacity of water is 4.18 J/gK or 4.18 kJ/kgK.
Alternatively, you could measure the specific heat capacity of a metal block using the same method – heat it with an electric heater connected to an ammeter and voltmeter, record its mass, the temperature change, the time taken for the temperature change to occur, and calculate the energy transferred using Q=IVt.
- Recall and use the equation:
Energy = mass x specific heat capacity x change in temperature
In other words,
Q = mcΔT.
Notes submitted by Sarah.
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