Specific Heat Capacity

Imagine walking along a hot beach: the sand feels hot, yet the nearby seawater feels cool. Both have been heated by the Sun for the same amount of time, so why do they feel so different? The answer lies in their specific heat capacities.

When a substance is heated (and it is not changing state), the energy transferred increases the kinetic energy of its particles, which causes its temperature to rise. However, different materials require different amounts of energy to raise their temperature.

The specific heat capacity of a substance tells you how much energy is needed to raise the temperature of of a substance by . Substances with a high specific heat capacity (like water) warm up slowly because they require more energy to increase their temperature. Substances with a low specific heat capacity (like sand) heat up quickly because they need much less energy.

The energy transferred to an object to increase it's temperature by is the same amount as the energy emitted by an object when it's temperature decreases by .

We can calculate the specific heat capacity of a substance using the following equation.

Formula:

We can use this equation to calculate how much energy is needed to bring of water at up to boiling point in a kettle, if we know the specific heat capacity of water is .

First, we need to convert by dividing by , so becomes .

Next, we need to find the change in temperature. Water will boil at , so the change in temperature will be:

Finally we will use the following equation:

We can find the specific heat capacity of solid, metal block by heating it with an electrical heater (immersion heater) and measuring the:

• The energy transferred using the Joulemeter

• The mass using a scale/balance

• The change in temperature using a thermometer

Method

• Use a balance to measure the mass of the metal block (ensure it reads zero before beginning).

• Set up the apparatus as shown above.

• Wrap the block in insulation to reduce energy loss to the surroundings.

• Measure and record the block's initial temperature using the thermometer.

• Switch on the power supply and start a stopwatch.

• Record the final temperature after and calculate the temperature change.

• Record the total energy transferred to the block using the joulemeter.

• Use the equation to find the specific heat capacity.

In some scenarios, you will not have a joulemeter available to you. In these cases, to find the energy supplied to the block, you need to measure the potential difference across the heater with a voltmeter, the current with an ammeter, calculate the power supplied using the equation,, and then multiply by the time to obtain the total energy supplied, . We can adapt the method by recording the block's temperature every 60 seconds and calculating the energy supplied at each interval to see how the data changes.

For example, if I wanted to find the specific heat capacity of a copper block, heated using an electric immersion heater that is connected to a voltmeter reading and an ammeter reading,, I could calculate the power supplied using the equation:

Then, I calculate the energy transferred by using to get the following results:

Next, we need to calculate the change in temperature, as at a time = , the temperature is this is the initial temperature.

The total energy transferred to the block in the experiment would be so we can calculate the specific heat capacity:

If you look up the specific heat capacity of copper online, you will find it is . Our calculated value is higher as some energy was dissipated to the surroundings, not all of the energy supplied went into heating the block.