The heat pump in a fridge uses a fluid with a high specific latent heat - Leaving Cert Physics - Question (b) - 2017

Specific latent heat is the amount of heat required to change the state of 1 kg of a substance without changing its temperature. It is essential during phase changes, such as from liquid to gas, where heat is absorbed or released.

To find the energy removed from the water as it cools, we can use the formula:

$Q = mc heta$

where:

• $Q$ is the heat energy removed (in Joules),
• $m$ is the mass of the water (2 kg),
• $c$ is the specific heat capacity of water (4200 J kg⁻¹ K⁻¹), and
• $heta$ is the change in temperature.

The change in temperature, $heta$, is:

$heta = T_{initial} - T_{final} = 30°C - 5°C = 25°C$

Now, substituting the values into the formula:

$Q = 2 ext{ kg} imes 4200 ext{ J kg}^{-1} ext{ K}^{-1} imes 25 ext{ K} = 210000 ext{ J}$

Power can be calculated using the formula:

$P = \frac{W}{t}$

where:

• $P$ is the power (in Watts),
• $W$ is the work done or energy removed (210000 J), and
• $t$ is the time taken (840 s).

Substituting the values:

$P = \frac{210000 ext{ J}}{840 ext{ s}} \approx 250 ext{ W}$