When Kate heats Bernard's tea, she uses a mind lens, an apparatus that helps focus magical power.
Mind lenses seem magical to us, but, if people used them every day, they'd be a lot like magnifying glasses, fun but not special.
There are lots of ways to heat things. On a sunny day, you might use a fresnel lens to heat liquid, but it would be awfully boring (and may not work unless you have a very large lens).
Another would be to use an exothermic reaction.
Exothermic reactions produce heat and you encounter them everywhere. Brushing your teeth, washing your hair, and lighting your stove are all examples of exothermic reactions.
thoughtco.com has this somewhat complicated explanation. It's worth reading if you take it slowly, and there's a simpler explanation after.
An exothermic reaction is a chemical reaction that produces heat (has a negative ΔH). In other words, the activation energy needed to start the reaction is less than the energy it releases. I.e. it gets hotter!
Examples of exothermic reactions include neutralisation reactions, the Haber process, the thermite reaction, and combustion reactions.
The opposite of an exothermic reaction is an endothermic reaction. Endothermic reactions absorb more heat from their surroundings than they release.
Exothermic and endothermic reactions are types of exergonic and endergonic reactions. In exergonic and endergonic reactions, the net energy (whether it be heat, light, or sound) is greater (exergonic) or less (endergonic) than the energy needed for the reaction to proceed.*
Exothermic: The reaction produces more heat than is needed to start the reaction and keep it going. Like when you burn wood in a fire. There’s more heat produced than is needed to keep the wood burning, so you get warm and the wood continues to burn. Of course burning wood is a “combustion reaction”. Combustion is also what’s going on inside your car (if it runs on petrol or diesel).
Endothermic: Produces less heat than is needed. Like when you melt ice. To keep the reaction going you need to keep applying heat.
Exothermic reactions can be very gentle producing just a little warmth (like those satchels that you put in your gloves to keep your hands warm), through to explosive (e.g. dynamite).
We’re going to try one of the gentle kind using either, steel wool and vinegar or clothes washing detergent. Both will work.
In this reaction, vinegar is used to remove the protective coating from steel wool, allowing it to rust (rusting is an example of oxidation) . When the iron combines with oxygen to form iron oxide (or rust), heat is released. This takes about 5- 15 minutes and doesn't produce much heat (so don't worry).
For this experiment you'll need:
Place the thermometer in the jar. Allow about 5 minutes for the thermometer to record the temperature, then read the thermometer. Note down the temperature.
Remove the thermometer from the jar.
Soak a piece of steel wool in vinegar for 1 minute.
Squeeze the excess vinegar out of the steel wool.
Wrap the steel wool around the thermometer and place the wool/thermometer in the jar
Allow 5 minutes, then read the temperature and compare it with the first reading. If you’re using a kitchen thermometer, you should see the temperature rising during the 5 minutes.
Not only does the vinegar remove the protective coating on the steel wool, but once the coating is off, its acidity aids in oxidation (rust) of the iron in the steel.
The thermal energy given off during this chemical reaction causes a temperature change.
In the rusting of iron, four atoms of solid iron react with three molecules of oxygen gas to form two molecules of solid rust (iron oxide).
When you add detergent to water, the powder breaks apart in the water (i.e., they dissolve). As it dissolves, the molecules of powder detach and mix with water molecules. This change in arrangement releases energy and causes a temperature change.
When the washing powder molecules release energy in the solution, it heats up.
Note that this change in energy happens whenever any solid dissolves in water, even table salt. Detergent is used in this experiment because it produces a measurable change using a small amount of powder.
Also note that technically no chemical reaction is occurring, the temperature changes because molecules are rearranging themselves and release energy as they do.
For this to work, the detergent must contain sodium carbonate (also called washing soda). You must check the ingredients.
You also need room temperature water. It's best to fill one of your jars with water and let it stand for 30 mins.
A clean jar with a water tight lid. A jam jar is fine. The jar should be large enough that you can add detergent and water without making a mess everywhere.
A spoon (it's best to use on that fits in your jar)
Place 3 spoons of water in the jar.
Take note of the temperature.
Next add 1 spoon of detergent.
Seal the jar with the lid and shake gently or stir with a spoon.
Carefully remove the lid (if you used it).
Now take the temperature again.
Try 2 different combinations.
For example 2 spoons of powder and 2 spoons of water or 1 spoon of powder and 6 spoons of water.
Note down the temperature change in each case. Explain the results.
Research and explain the heat production process for steel wool and vinegar and washing powder.
Steel wool and vinegar is an example of oxidation. What are other examples of oxidation?
Oxygen is super important, it keeps you alive after all. What is it about oxygen that makes it so important? Why is it so reactive?
*Helmenstine, Anne Marie, Ph.D. "Exothermic Reaction Definition." ThoughtCo, Aug. 26, 2020, thoughtco.com/definition-of-exothermic-reaction-604462.
*Helmenstine, Anne Marie, Ph.D. "How to Create an Exothermic Chemical Reaction." ThoughtCo, Aug. 25, 2020, thoughtco.com/create-an-exothermic-chemical-reaction-602208.