Molecules and matter: Chapter 6

Question 1

Which two quantities do you need to measure to find the density of a solid or liquid?

Answer 1

Mass and volume

Question 2

What happens to the particles in a substance if its temperature increased?

Answer 2

They move faster and the energy in their kinetic energy store increases.

Question 3

Why are changes of state physical changes?

Answer 3

No new substances are produced and the substance will have the same properties as before if the change is reversed.

Question 4

Why is the mass of a substance conserved when it changes state?

Answer 4

The number of particles does not change.

Question 5

What is the internal energy of a substance?

Answer 5

The total kinetic energy and potential energy of all the particles of the substance.

Question 6

Why does a graph showing the change in temperature as a substance cools have a flat section when the substance is changing shape?

Answer 6

The energy transferred during a change in state causes s change in the internal energy of the substance.

Question 7

What is the name given to the energy transferred when a substance changes state?

Answer 7

Latent heat

Question 8

What is the specific latent heat of a substance?

Answer 8

The energy required to change the state if one kilogram of that substance with no change in temperature.

Question 9

What is the specific latent heat of fusion of a substance?

Answer 9

The energy required to change one kilogram of the substance from solid to liquid at its melting point, without changing its temperature.

Question 10

What is the specific latent heat vaporisation of a substance?

Answer 10

The energy required to change one kilogram of the substance from liquid to vapour at its boiling point, without changing its temperature.

Question 11

On a graph of the temperature against time for a substance being up or cooled down, what do the flat (horizon) sections show?

Answer 11

The time when the substance is changing state and the temperature is changing.

Question 12

What property of a gas is related to the average kinetic energy of its particles?

Answer 12

Temperature.

Question 13

Why does density change when a substance changes state?

Answer 13

When a substance changes state the mass stays the same but the volume changes. Since density is dependent on mass AND volume it changes.

Question 14

What is a linear and non-linear relationship between two quantities?

Answer 14

If a graph is plotted and the line of best fit is straight then we say that there is a linear relationship between the two quantities on the x and y axes. If the line is not straight then it is non-linear.

Question 15

What is meant by a directly proportional relationship between two quantities?

Answer 15

If a graph is plotted and the line of best fit is straight and goes through the origin then there is a directly proportional relationship between the two quantities.

Question 16

What is the spring constant?

Answer 16

The spring constant is the amount of force needed to stretch (or compress) a material by 1 m. Its unit is N/m.

Question 17

How do you determine spring constant from a force extension graph?

Answer 17

The spring constant is the gradient of the straight part of a force-extension graph when force is on the y-axis and extension on the x-axis.

Question 18

What is the relationship between force, spring constant, and extension?

Answer 18

Force = spring constant × extension
F = ke

Question 19

What are the units for the force, spring constant, and extension equation?

Answer 19

Force (Newtons, N), Spring constant (Newtons per metre, N/m), Extension (metres, m)

Question 20

What is Hooke’s law?

Answer 20

The extension of a material is directly proportional to the force applied up to the limit of proportionality (elastic limit)

Question 21

On a force extension graph where is the limit of proportionality

Answer 21

The limit of proportionality on this graph is where the line stops being straight. It is the point at which it begins to curve.

Question 22

What is meant by elastic deformation?

Answer 22

An object which is stretched (or compressed) will return to its original length when the force is removed if it hasn’t passed the limit of proportionality.

Question 23

What is meant by inelastic deformation?

Answer 23

An object which is stretched (or compressed) will not return to its original length when the force is removed if it has passed the limit of proportionality. There will be permanent deformation.

Question 24

How do you carry out a force extension experiment accurately?

Answer 24

1. Set up a clamp stand with a spring.
2. Clamp a ruler making sure it is vertical with a set square.
3. Make sure the zero of the ruler is at the bottom of the spring.
4. Add masses and record the extension of the ruler each time.
5. Make sure to measure the extension at eye-level.

Question 25

What is the relationship between mass, volume, and density?

Answer 25

density = mass/volume
ρ = m/V

Question 26

What do we mean by the resolution of a measuring instrument?

Answer 26

The resolution of a measuring instrument is the smallest change that can be read from that instrument e.g. 1 mm on a ruler, or 1° on a protractor.