States of Matter & Thermal Capacity Flashcards

All 56 cards in this deck

What is the equation for density?

density $=$ mass $\div$ volume
$\rho = m / V$, with mass in kg and volume in m$^3$ giving kg/m$^3$.

What is the SI unit of density, and what other unit is often used?

kg/m$^3$; g/cm$^3$ is also used.

What are the steps to find the mass of an object from its density and volume?

e.g. density $2000$ kg/m$^3$, volume $3$ m$^3$

1. Rearrange: mass $=$ density $\times$ volume
2. Substitute: $2000 \times 3$
3. Mass $= 6000$ kg

What are the steps to convert a density in g/cm$^3$ into kg/m$^3$?

e.g. $2.7$ g/cm$^3$

1. Multiply the value by $1000$: $2.7 \times 1000$
2. Density $= 2700$ kg/m$^3$

What is the density of water in kg/m$^3$ and in g/cm$^3$?

$1000$ kg/m$^3$, which is $1$ g/cm$^3$.

True or false? A large object always has a greater density than a small object.

False. Density depends on mass divided by volume, so a large light object can be less dense than a small heavy one.

Using the kinetic theory model, describe the arrangement and movement of particles in a solid.

Particles are closely packed in a regular arrangement and vibrate about fixed positions.

Using the kinetic theory model, describe the arrangement and movement of particles in a liquid.

Particles are close together but randomly arranged, and can move past one another.

Using the kinetic theory model, describe the arrangement and movement of particles in a gas.

Particles are far apart and randomly arranged, moving quickly in all directions.

In terms of particle spacing, why is a substance much less dense as a gas than as a liquid?

Its particles are much further apart, so the same mass fills a far larger volume.

Which state of matter usually has the highest density, and why in terms of particles?

The solid state, because the particles are packed most closely together.

True or false? Water is unusual because it is less dense as a solid (ice) than as a liquid.

True. Ice floats on water, whereas most substances are denser as a solid.

What are the steps to determine the density of a regular solid such as a cuboid?

e.g. a block $2$ cm $\times$ $3$ cm $\times$ $5$ cm of mass $60$ g

1. Measure mass on a balance: $60$ g
2. Measure the sides with a ruler and calculate volume: $2 \times 3 \times 5 = 30$ cm$^3$
3. Density $=$ mass $\div$ volume $= 60 \div 30 = 2$ g/cm$^3$

What are the steps to determine the density of an irregular solid using water displacement?

e.g. a stone of mass $60$ g

1. Measure the mass on a balance: $60$ g
2. Lower it into a measuring cylinder (or displacement can) of water and find the volume of water displaced: $20$ cm$^3$
3. Density $=$ mass $\div$ volume $= 60 \div 20 = 3$ g/cm$^3$

What are the steps to determine the density of a liquid using a balance and a measuring cylinder?

e.g. empty cylinder $50$ g; with $20$ cm$^3$ of liquid $66$ g

1. Find the mass of the liquid by subtracting: $66 - 50 = 16$ g
2. Read the volume from the cylinder: $20$ cm$^3$
3. Density $=$ mass $\div$ volume $= 16 \div 20 = 0.8$ g/cm$^3$

True or false? When finding the density of a liquid, the balance reading of the liquid in the measuring cylinder can be used as the mass of the liquid.

False. The mass of the empty measuring cylinder must be subtracted first.

How should a measuring cylinder be read to avoid a parallax error?

With the eye level with the bottom of the meniscus.

What is sublimation?

A substance changing directly from solid to gas without becoming a liquid.

What name is given to the change from gas to liquid?

Condensing (condensation).

Which change of state is the reverse of melting, and at what temperature does it happen?

Freezing, at the same temperature as the melting point.

What happens to the mass of a substance when it melts, boils, condenses or sublimates?

Mass is conserved — it stays the same, because no particles are created or destroyed.

How does a physical change of state differ from some chemical changes?

A change of state is reversible — the material recovers its original properties if the change is reversed.

True or false? When water in an open beaker boils away, mass has been lost.

False. Mass is conserved; the water has become steam of the same mass, which has escaped into the air.

What two things can happen when a system is heated?

Its temperature rises, or it changes state.

What happens to the energy stored in a system when it is heated?

The energy in its thermal (internal) energy store increases, so the particles move faster or are pulled further apart.

What is the energy supplied to a substance used for during a change of state?

Breaking the forces of attraction between particles (separating them), not raising the temperature.

True or false? While a substance is changing state, its temperature stays constant even though energy is still being supplied.

True. The energy separates the particles instead of raising the temperature.

What happens to energy and temperature when steam condenses to water at $100$ °C?

Energy is transferred from the substance to the surroundings while the temperature stays constant.

Define specific heat capacity.

The energy needed to raise the temperature of $1$ kg of a substance by $1$ °C.

Define specific latent heat.

The energy needed to change the state of $1$ kg of a substance with no change in temperature.

What is the key difference between specific heat capacity and specific latent heat?

Specific heat capacity involves a temperature change with no change of state; specific latent heat involves a change of state at constant temperature.

True or false? Supplying the specific latent heat to $1$ kg of ice at $0$ °C makes its temperature rise.

False. It melts the ice at $0$ °C with no temperature change.

What is the equation for the change in thermal energy when a substance's temperature changes?

change in thermal energy $=$ mass $\times$ specific heat capacity $\times$ change in temperature
$\Delta Q = m \times c \times \Delta\theta$

What are the units of specific heat capacity?

J/kg °C (joule per kilogram degree Celsius).

What is the specific heat capacity of water?

$4200$ J/kg °C.

In the equation $\Delta Q = m \times c \times \Delta\theta$, what unit must the mass be in?

Kilograms (kg) — a mass in grams must be divided by $1000$ first.

What are the steps to calculate specific heat capacity from energy, mass and temperature rise?

e.g. $8400$ J raises $1$ kg of a liquid by $2$ °C

1. Write $\Delta Q = m \times c \times \Delta\theta$
2. Rearrange: $c = \Delta Q \div (m \times \Delta\theta)$
3. Substitute: $c = 8400 \div (1 \times 2) = 4200$ J/kg °C

True or false? A substance with a high specific heat capacity needs less energy to raise the temperature of $1$ kg by $1$ °C.

False. A high specific heat capacity means more energy is needed per kilogram per degree.

What is the equation for the thermal energy needed for a change of state?

thermal energy $=$ mass $\times$ specific latent heat
$Q = m \times L$

What are the units of specific latent heat?

J/kg (joule per kilogram).

Which changes of state use the specific latent heat of fusion?

Melting and freezing (solid ↔ liquid).

Which changes of state use the specific latent heat of vaporisation?

Boiling/evaporating and condensing (liquid ↔ gas).

What are the steps to calculate the thermal energy needed to melt a mass of ice?

e.g. $0.5$ kg of ice at $0$ °C, $L = 3.34 \times 10^5$ J/kg

1. Write $Q = m \times L$ with mass in kg
2. Substitute: $Q = 0.5 \times 3.34 \times 10^5$
3. $Q = 1.67 \times 10^5$ J

What are the steps to calculate a specific latent heat from energy and mass?

e.g. $4.6$ MJ turns $2$ kg of boiling water into steam

1. Write $Q = m \times L$
2. Rearrange: $L = Q \div m$
3. Substitute: $L = 4.6 \div 2 = 2.3$ MJ/kg

What is a thermal insulator?

A material that is a poor conductor of thermal energy, so it reduces the rate of energy transfer.

Name three ways of reducing unwanted energy transfer from a house.

Loft insulation, cavity wall insulation and double glazing (also draught excluders, thicker walls, carpets).

What property of cavity wall insulation reduces energy transfer through a wall?

It traps air in foam or fibre, which is a poor conductor and stops convection currents in the cavity.

How do the thickness and thermal conductivity of a wall affect the rate of energy transfer through it?

Thicker walls and a lower thermal conductivity both give a slower rate of energy transfer.

True or false? Double glazing reduces energy transfer because the air gap between the panes is a poor conductor.

True. Trapped air (or a vacuum) between the panes slows conduction through the window.

State the three measurements needed to calculate the specific heat capacity of water in the core practical.

The mass of the water, the temperature rise (start and end temperatures), and the energy supplied by the heater (joulemeter reading).

What are the steps of the core practical to determine the specific heat capacity of water?

e.g. using $1$ kg of water and an immersion heater

1. Measure the mass of water in an insulated container and record its starting temperature
2. Switch on the heater (joulemeter connected); record the energy supplied and the final temperature
3. Calculate $c = \Delta Q \div (m \times \Delta\theta)$

State two ways the specific heat capacity apparatus could be adapted to improve the procedure.

Add a lid and add lagging/insulation (also: add a stirrer, use a more sensitive/digital thermometer, ensure the heater is fully submerged).

What is the main source of error in the specific heat capacity of water experiment, and its effect on the result?

Energy lost to the surroundings, which makes the calculated specific heat capacity too high.

On a temperature–time graph for ice being heated, what does the flat plateau at $0$ °C show?

The ice is melting — the energy supplied is changing the state, not raising the temperature.

At what temperature does the temperature–time graph for water being heated level off again, and why?

At about $100$ °C, because the water is boiling (changing state to steam).

True or false? When a solid is heated until it becomes a gas, its particles get bigger.

False. The particles stay the same size; they simply move faster and become much further apart.