Heating and cooling curves

Question 1

What do heating and cooling curves do?

Answer 1

Heating and cooling curves model changes of state like when a solid changes into a liquid (melting) or when a gas changes into a liquid (condensing).

Question 2

solid—-> liquid=?

Answer 2

melting

Question 3

gas—>liquid

Answer 3

condensing

Question 4

What is a heating and cooling curve?

Answer 4

A heating or cooling curve is a simple line graph that shows the phase changes a given substance undergoes with increasing or decreasing temperature.

Question 5

What is the y axis?

Answer 5

temperature is measured on the vertical y-axis

Question 6

What is the x-axis?

Answer 6

the amount of heat added over time is measured on

the horizontal x-axis.

Question 7

In general what goes up the longer the heating continues

Answer 7

The temperature goes up the longer the heating continues

Question 8

What occurs when there is a change of state? (in terms of the graph)

Answer 8

two horizontal flat parts of the graph

Question 9

What happens when a substance melts? (temp)

Answer 9

The temperature stays the same while a substance melts (0 degrees celsius for water)

Question 10

What happens when a substance boils?

Answer 10

The temperature stays the same for while a substance boils (100 degrees celsius for water)

Question 11

What happens when a substance is heated?

Answer 11

When heated, the substance absorbs the energy. This, then, causes the system to change its state. For instance, a substance in a solid-state will change into another state, e.g. liquid state, as it absorbs heat energy.

Question 12

When is a plateau reached?

Answer 12

A plateau is reached when the substance reaches the melting point, i.e. changing from solid to liquid.

Question 13

When is a plateau reached, does the temperature change?

Answer 13

No, the temperature does not change. The heat supplied is being used up in changing the state of the substance by overcoming the forces of attraction between the particles.

Question 14

What happens to the substance as it melts and boils

Answer 14

The temperature of a substance remains constant at its melting and boiling points until all the substance melts or boils.

Question 15

What happens with a further increase of temperature in a substance that turned into a liquid?

Answer 15

With further increase in temperature, the substance that turned into liquid will turn into gas as it absorbs energy.

Question 16

Pure substances have…?

Answer 16

Pure substances have specific melting, freezing and boiling points.

Question 17

A substance (solid) containing impurities usually…

Answer 17

melts at a lower temperature than the pure compound. It can also melt over a wide range of temperatures.

Question 18

What happens when an impurity is added to a liquid,

Answer 18

its boiling point is elevated i.e. its boiling point is increased.

Question 19

What is the melting/ freezing point?

Answer 19

the melting point or freezing point is the temperature at which the solid and liquid phases of a substance can exist in equilibrium.

Question 20

For pure substances the opposite of melting point is

Answer 20

the freezing point

Question 21

For pure substances the opposite of boiling point is

Answer 21

The point of condensation

Question 22

What is latent heat?

Answer 22

the energy absorbed or released by a substance

during a change in its physical state (phase) that occurs without changing its temperature.

Question 23

The latent heat associated with melting a solid is called what?

Answer 23

the heat of fusion.

Question 24

What is the heat of fusion?

Answer 24

It is the amount of heat required to change a substance at the temperature of its melting point from the solid to the liquid state without changing temperature.

Question 25

That associated with vaporizing a liquid is called what?

Answer 25

the heat of vaporization.

Question 26

What is the heat of vaporization?

Answer 26

It is the amount of heat required for the

transformation of a liquid at its boiling point to gas at a constant temperature.

Question 27

Latent heat arises from what?

Answer 27

the energy required to overcome the forces that hold together atoms or molecules in a material.