Changing State (pg 121)

Question 1

Physical changes don’t change the particles, so what changes?

Answer 1

Just their arrangement or their energy

Question 2

When a solid is heated, what happens?

Answer 2

Its particles gain more energy

Question 3

When particles are heated and gain more energy, what happens to the particles?

Answer 3

they vibrate more, which weakens the forces that hold the solid together.

Question 4

At a certain temperature, called the melting point, the particles have enough energy to break free from their positions. What is this called?

Answer 4

This is called MELTING and the solid turns into a liquid

Question 5

What happens when a liquid is heated?

Answer 5

again the particles get even more energy

Question 6

What happens when the liquid particles have even more energy?

Answer 6

the particles move faster, which weakens and breaks the bonds holding the liquid together.

Question 7

At a certain temperature, called the boiling point, the particles have enough energy to break their bonds, what is happening at this point?

Answer 7

This is Boiling (or evaporating). The liquid becomes a gas

Question 8

As a gas cools, what happens regarding the particles?

Answer 8

the particals no longer have enough energy to overcome the forces of attraction between them. so Bonds form between the particles

Question 9

At the BOILING POINT, so many bonds have formed between the gas particles, that the gas becomes a liquid, what is this called?

Answer 9

Condensing

Question 10

When a liqud cools what happens to the particles?

Answer 10

the particles have LESS ENERGY, so move around less.

There’s not enough energy to overcome the attraction between the particles so more bonds form between them

Question 11

At the melting point, so may bods have formed between the particles that they’re held in place. The liquid becomes a solid, what is the name of this?

Answer 11

This is FREEZING

Question 12

How much energy is needed for a substance to change state?

Answer 12

This depends on how strong the forces between the particles are.

The stronger the forces, the more energy is needed to break them, and so the higher the melting and boiling points of the substance

Question 13

In an exam, you might be asked to predict what state a substance is in at a certain temperature.

So if the temperature’s BELOW the melting point of substance, what state will it be in?

Answer 13

It will be a solid

Question 14

If a substance is above the boiling point, what state will it be in?

Answer 14

It will be a gas.

Question 15

If a substance is IN-BETWEEN the two points what state is it in?

Answer 15

It is a liquid

(the bulk properties such as the melting point of a material, depend on how lots of atoms interact together. An atom on its own doesn’t have these properties)

Question 16

Which of the molecular substances below, are a liquid at room temperature (25°C)?

                                 Melting Point            Boiling Point

Oxygen -219°C -183°C
Nitrogen -210°C -196°C
Bromine -7°C 59°C

Answer 16

Oxygen and nigrogen have boiling points below 25°C, so will both be gasses at room temperature

So the answer’s BROMINE. It melts at -7°C and boils at 59°C, So it’ll be a liquid at room temperature

Question 17

For an exam, make sure you can describe what happens to particles, and the forces between them, as a substance is heated and cooled. Then learn all the technical terms.

Ethanol melts at -114°C and boils at 78°C. Predict the state that ethanol is in at:

a) -150°C
b) 0°C
c) 25°C
d) 100°C

Answer 17

a) Solid
b) Liquid
c) Liquid
c) Gas