MediumChemistryHigh School (9–10)GeneralStates of Matter › Change of StateConceptualNumericalBoard Exam

The graph shows 1 kg of ice heated until it becomes steam…

Try it on paper first. A hint, the key idea and the worked solution are here when you need them.

A graph of temperature against the heat added to 1 kg of ice. The line rises from minus 20 degrees to 0, then is flat at 0 degrees for 334 kJ while the ice melts. It then rises to 100 degrees, is flat at 100 degrees for 2260 kJ while the water boils, and then rises again as steam.

The graph shows $1\ \text{kg}$ of ice heated until it becomes steam.

What are the temperatures of the two flat parts, and what is happening along each?
The same is done with $2.5\ \text{kg}$ of ice. How much heat do the two flat parts take now, in kJ?

Need a reminder? The key ideaShow

During a change of state the temperature stays the same while heat goes in or comes out: the latent heat. $Q = mL$ , with $L_f = 3.34 \times 10^{5}\ \text{J/kg}$ to melt ice and $L_v = 2.26 \times 10^{6}\ \text{J/kg}$ to boil water. To warm water, $Q = m \times 4180\ \text{J/(kg}\,^\circ\text{C)} \times \text{(the rise)}$ .

The worked solution

Have you tried it?

Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.

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