About this blog

Physics can be difficult to learn, but this blog aims to help you get into physics by connecting your GCSE physics lessons with things you see in the world around you.

Friday, 16 September 2011

Breaking Bonds

Sometimes the things we see around us are as plain as the noses on our faces, like rain beating down, day turning into night and the autumn leaves changing, although they are all made by forces we can’t see in action. Changes can happen on all levels from the large scale like planets moving and rotating, to the molecular level. And that is where our journey takes us today.

Let’s start with ice. Great in drinks on a hot day, as it keeps them nice and cool. But have you ever thought why it’s better to have ice rather than just a really chilled drink? The secret is in the bonds that form the solid.

When water changes to ice, the molecules move into a strong fixed structure, and it takes a lot of energy to reverse the process. This energy needs to be in the form of heat, so the ice extracts a lot of heat from wherever it can (in this case your drink) to get enough energy to return to water. This is called Latent Heat because it’s hidden.

It’s hidden because it doesn’t show up on the thermometer. If you take a block of ice and start heating it up, you’ll find that the temperature increases to zero quite quickly, but then remains at zero for quite some time despite the fact that you’re still heating the ice. This is because the energy is going to break the bonds so the ice is changing from a solid at 0°C to a liquid at the same temperature.

The same happens again when you hit the boiling point of 100°C because the bonds once more have to be broken so that the molecules can escape the water and become water vapour.

So next time you have ice in your drink, spare a thought for all the work that’s going on just to keep your drink cold!

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