P6 Molecules and matter

Question 1

What is density?

Answer 1

The density of a substance is defined as its mass per unit volume.
density=mass (kg)/volume (m cubed)

Question 2

Converting units and using standard form

Answer 2

1kg=1000g
1m=100cm
1m cubed=1000000cm cubed
1000kg/m cubed=1g/cm cubed

Question 3

How to find the density of a solid object?

Answer 3

1) Use a balance to measure its mass.
2) If it’s a regular solid, start by measuring its length, width and height with a ruler. Calculate its volume using formula for that shape.
3) For an irregular solid, you can find its volume by submerging it in a eureka can filled with water. The water displaced by the object will be transferred to the measuring cylinder.
4) Record the volume of water in the measuring cylinder as the volume of the object.
5) Plug the object’s mass and volume into the formula above to find its density.

Question 4

How to find the density of a liquid?

Answer 4

1) Place a measuring cylinder on a balance and zero the balance.
2) Pour 10ml of the liquid into the measuring cylinder and record the liquid’s mass.
3) Pour another 10ml into the measuring cylinder, repeating the process until the cylinder is full and recording the total mass and volume each time.
4)For each measurement, use the formula to find the density. 1ml=1cm cubed
5) Take an average of your calculated densities to give you a value for density of the liquid.

Question 5

Conservation of mass

Answer 5

The mass of the substance is conserved when it changes its state. For example, when a given mass of ice melts, the water it turns into has the same mass so the mass of the substance stays unchanged.

Question 6

Solids

Answer 6

strong forces of attraction hold the particles close together in a fixed, regular arrangement. The particles don’t have much energy so they can only vibrate about heir fixed positions. Highest density as the particles are closest together.

Question 7

Liquids

Answer 7

Weaker forces of attraction between the particles. The particles are close together but can move past each other and form irregular arrangements. More energy than particles in a solid-move in random directions at low speeds less dense than solids

Question 8

Gases

Answer 8

no forces of attraction between the particles. The particles have more energy than in liquids and solids as they are free to move and travel in random directions at high speeds. Less dense than liquids

Question 9

Changes of state graph
Melting

Answer 9

The energy is being used to break intermolecular forces that hold molecules in place
internal potential energy increases on melting

Question 10

Heating up

Answer 10

sloping parts on graph show increase in temperature
the internal kinetic energy increases as the temperature increases

Question 11

Boiling

Answer 11

The energy is being used to break intermolecular forces that hold liquid molecules in place. The internal potential energy increases on evaporation.

Question 12

Specific Latent Heat

Answer 12

The specific latent heat of a substance is the amount of energy needed to change 1kg of it from one state to another without changing its temperature.
For cooling, specific latent heat is the energy released by a change in state.

Question 13

What is the specific latent heat for changing between a solid and liquid called?

Answer 13

Specific Latent Heat of fusion

Question 14

What is the specific latent heat for changing between a liquid and a gas called?

Answer 14

specific latent heat of vapourisation

Question 15

What is the internal energy?

Answer 15

The internal energy is the energy of the particles that is caused by the individual motion and positions. The internal energy of the particles is the sum of the kinetic energy they have due to their individual motions relative to each other and the potential energy they have due to their individual positions relative to each other.

Question 16

When heating a substance, how does the change in internal energy of the substance change?

Answer 16

Heating a substance changes the internal energy of the substance by increasing the energy of its particles as the temperature of the substance increases. When the temperature of a substance increases, the total kinetic energy of its particles increases. When the physical state of a substance changes, the total potential energy of its particles changes.

Question 17

Why does the pressure of a gas increase when heated?

Answer 17

When a gas is heated, its particles gain kinetic energy and move faster. This causes the pressure of the gas to increase because the particles collide with the container surface more often and with more force.

Question 18

Why does increasing the temperature of any sealed gas container increase the pressure of the gas inside it?

Answer 18

This is because the energy transferred to the gas when it is heated increases the energy of its molecules so the average kinetic energy of the gas molecules increases when the temperature of the gas is increased. The average speed of the molecules increases when the kinetic energy increases and the molecules on average hit the container surfaces with more force and more often so the pressure of the gas increases.

Question 19

What happens if temperature is constant and you increase the volume of gas?

Answer 19

Increasing the volume of a gas means the particles get more spread out and hit the walls of the container less often so the gas particles decreases.

Question 20

Pressure and volume

Answer 20

Pressure and volume are inversely proportional. For a gas of fixed mass at constant temperature, pV=constant

Question 21

Boyle’s Law

Answer 21

pressure x volume= constant
For a fixed mass of gas at a constant temperature, its pressure is increased if its volume decreased and reducing the volume of a gas increases the number of molecular impacts per second on the surfaces that are in contact with the gas. The temperature of a gas can be increased if its compressed rapidly because work is done on it and the energy isnt transferred quickly enough to the surroundings.

Question 22

Why when released does a helium balloon rise?

Answer 22

Atmospheric pressure decreases with height so the pressure outside the balloon decreases. This causes the balloon to expand until the pressure inside drops to the same as atmospheric pressure.