Interpreting Heating Curves

Interpreting Heating Curves

By Amy Dahl

​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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A heating curve looks like this

You may not instantly know the answer

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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​More logic

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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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Let's try some!

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Multiple Choice

Describe the substance between letters C and D. 

• Gas
• Liquid
• Melting
• Vaporizing

Multiple Choice

Between which points is the temperature of the substance remaining constant?

• A-B only. 
• A-B, C-D, E-F
• B-C only. 
• B-C, D-E

Multiple Choice

True or false: melting and freezing occur at the same temperature.

• True
• False

Multiple Choice

Describe the substance between letters A and B. 

• Solid
• Liquid
• Melting
• Vaporizing

Multiple Choice

Describe what is happening between letters D and E. 

• Gas
• Liquid
• Melting
• Vaporizing

Multiple Choice

Describe the substance between letters E and F. 

• Gas
• Liquid
• Melting
• Vaporizing

Multiple Choice

What is the melting point for this substance?

• 60 °C
• 40 °C
• 80 °C
• 100 °C

Multiple Choice

What is the freezing point for this substance?

• 60 °C
• 40 °C
• 80 °C
• 100 °C

Multiple Choice

What is the boiling point for this substance?

• 60 °C
• 40 °C
• 120 °C
• 100 °C

Multiple Choice

What line segment represents only the solid state?

• A-B
• B-C
• C-D
• D-E

Multiple Choice

In which segment is the particle speed remaining constant?

• A-B
• B-C
• C-D
• E-F

Multiple Choice

What state(s) of matter are present at D-E?

• Solid-liquid
• Liquid
• Liquid-gas
• Gas-Solid

Multiple Choice

A substance's heating curve is shown in the graph.  What is its boiling point?

• 100 C
• 60 C
• 80 C
• 20 C

Multiple Choice

Which of the following terms identifies the change from a liquid to gas?

• Vaporization
• Condensation
• Deposition
• Sublimation

Multiple Choice

When the temperature of matter increases the particles...

• speed up and move closer
• speed up and move farther apart
• slow down and move closer together
• slow down and move farther apart

Multiple Choice

From point A to point E, the sample is going through an

• exothermic process by releasing heat to the surroundings

• exothermic process by absorbing heat from the surroundings

• endothermic process by releasing heat to the surroundings

• endothermic process by absorbing heat from the surroundings

Multiple Choice

The melting point of the sample is

• -60 ºC

• -100 ºC

• 60 ºC

• 100 ºC

Multiple Choice

Evaporation is what kind of change?

• Endothermic
• Exothermic