Up Learn – A Level physics (AQA) – THERMAL PHYSICS
Specific Latent Heat – Worked Example
Calculating energy transferred using specific heat capacity and specific latent heat of fusion.
Here we have 2.5 kilograms of ice, which has a temperature of -30 degrees Celsius.
When we place a heater beneath the ice, the temperature of the ice increases to 0 degrees Celsius…
And the ice melts.
If we take the heater away the moment the ice has melted…
And we assume that no energy is transferred to or from the surroundings…
What is the total energy transferred to the ice?
Now, two things happen in this example.
First, the temperature of the ice increases to 0 degrees Celsius…
And then, the ice undergoes a state change.
So, let’s take a look at each process separately, starting with the temperature increase.
Now, we’ve seen that we can calculate the energy required to increase the temperature of a substance using this formula
And so, if this specific heat capacity of ice
What is the value of Q?
To work out the value of Q, we list out the variables we know…
Where, to find the change in temperature, we subtract the initial temperature from the final temperature.
We then substitute the values into the formula
And calculate to find that the value for Q is this.
So, now that we know how much energy was transferred to increase the temperature of the ice…
We next need to work out how much energy was transferred to change the ice into liquid water
Which we can do using this formula.
And so, if the specific heat of fusion for ice is this…
What is the value of Q here?
To work out the value of Q, we substitute these values into the equation…
And calculate to find that Q equals this!
So now we know how much energy was transferred to increase the temperature of the ice…
And how much was transferred to change it from a solid to a liquid.
This means that the total energy transferred to the ice is equal to this..
So, all we need to do is add these two values together!
And so, what is the total energy supplied to the ice?
Adding these two values together, we calculate that the total energy transferred to the ice is this!