Interpreting Heating Curves

​It shows a plot of temperature at various times as a substance is heated.

It is notable for having two "flat spots" where the temperature remains constant even though heat continues to be added.​

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Use what you know to figure out the answer!

The "flat spots" are the key. We can use them to reason out the answer to any question having to do with heating curves.

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The vertical axis is temperature.​ So the higherr the curve gets, the higher the temperature.

Temperature is a measure of particle speed. The higher the temp, the faster they move.​

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First, notice the axes

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The horizontal axis is heat added (sometimes it is labeled time, but you know it is being heated the entire time).​

The farther you go to the right, the more energy has been added.​

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First, notice the axes

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We expect temperature to go up when the substance is being heated.

But from B-C and D-E it doesn't!

This is because temperature does not change when the phase is changing​.

​So during flat spots, the phase is changing. Always.

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​Next, the flat spots!

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Use logic to determine which flat spot is which.

Phase changes that occure when something gets heated are melting and vaporization.​

You know melting occurs at a lower temp than vaporization.

Thus B-C is melting, D-E is vaporization.​

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​Which is which?

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This heating curve, for water, shows water's melting point of 0 ^oC and its boiling point of 100 ^oC.

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Other substances have different melting and boiling points. Just read them off the temp scale.​

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Melting and boiling points

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Since melting is a change from solid to liquid, before melting you have a solid, and after melting you have a liquid.

So A-B is solid and C-D is liquid.

(during B-C both solid and liquid are present).

Since A-B and C-D slope upwards, T increases and we say they are warming up!​

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Since vaporization is a change from liquid to gas, before vaporization you have a liquid, and after vaporization you have a gas (vapor).

So C-D is liqulid and E-F is gas.

(during D-E both liquid and vapor are present).

Like A-B and C-D, E-F slopes upwards, so the gas gets hotter with time and we say it is warming up.

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​Similarly

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