A) Define heat capacity. b) Describe an experiment to determine the specific latent heat of steam.

Here's the solution to question 13.

Question 13:

a) Define the term heat capacity.

Heat capacity is the amount of heat energy required to change the temperature of a body by one degree Celsius (or one Kelvin).

b) Describe an experiment to determine the specific latent heat of steam, using the set up in Fig 5 and stopwatch. Clearly explain the measurements to be made and how these measurements could be used to determine $L_v$ (latent heat of vaporization).

Experiment Description:

1. Place a known mass of water in a lagged calorimeter (to minimize heat loss).
2. Immerse an electric heater of known power $P$ and a thermometer into the water.
3. Heat the water to its boiling point ($100\,^{\circ}\text{C}$).
4. Once the water is boiling steadily, use the scale balance to record the initial mass of the calorimeter and its contents ($m_1$).
5. Simultaneously start the stopwatch and allow the water to boil for a measured time $t$, during which steam escapes.
6. After time $t$, switch off the heater and stop the stopwatch.
7. Immediately record the final mass of the calorimeter and its contents ($m_2$) using the scale balance.

Measurements to be made:

• Initial mass of the calorimeter and water, $m_1$ (in kg).
• Final mass of the calorimeter and water, $m_2$ (in kg).
• Time of heating, $t$ (in seconds).
• Power of the electric heater, $P$ (in Watts).

Calculation of $L_v$:

1. The mass of steam evaporated during the time $t$ is calculated as the difference between the initial and final masses: $$m = m_1 - m_2$$
2. The electrical energy supplied by the heater during this time is given by: $$Q = P \times t$$
3. Assuming that all the electrical energy supplied is used to vaporize the water (due to the lagging), the heat supplied is equal to the heat absorbed by the steam: $$Q = m L_v$$
4. By equating the two expressions for $Q$, we can determine the specific latent heat of vaporization, $L_v$: $$P \times t = (m_1 - m_2) L_v$$ $$L_v = \frac{P \times t}{m_1 - m_2}$$ The unit for $L_v$ will be Joules per kilogram ($\text{J/kg}$).