Changes of State & the Particle Model Flashcards

All 24 cards in this deck

What is the equation linking density, mass and volume?

$\text{density} = \dfrac{\text{mass}}{\text{volume}}$ or $\rho = \dfrac{m}{V}$

In the density equation, what are the SI units of density, mass and volume?

Density in $\mathrm{kg/m^3}$, mass in $\mathrm{kg}$, volume in $\mathrm{m^3}$.

What are the steps to calculate the density of an object?

e.g. mass $= 30$ g, volume $= 10$ cm$^3$

1. Check the units match: g with cm$^3$ gives g/cm$^3$.
2. Divide mass by volume: $30 \div 10$.
3. Density $= 3$ g/cm$^3$.

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

e.g. density $= 2$ g/cm$^3$, mass $= 10$ g

1. Write the equation: $\rho = \dfrac{m}{V}$, so $2 = \dfrac{10}{V}$.
2. Rearrange: $V = \dfrac{m}{\rho} = \dfrac{10}{2}$.
3. Volume $= 5$ cm$^3$.

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

e.g. $2.5$ g/cm$^3$

1. Multiply the number by $1000$: $2.5 \times 1000 = 2500$.
2. Write the new unit: $2500$ kg/m$^3$.

True or false? If a block of aluminium is cut in half, each half has half the density of the whole block.

False. Density is unchanged — both the mass and the volume are halved.

How are the particles arranged in a solid?

Closely packed in a regular arrangement, vibrating about fixed positions.

How are the particles arranged in a liquid?

Closely packed but in a random arrangement, able to move past each other.

How are the particles arranged in a gas?

Far apart and randomly arranged, moving quickly in all directions.

Why is a gas much less dense than the same substance as a liquid or solid?

Its particles are much further apart, so there is far less mass in the same volume.

For most substances, which state of matter has the highest density, and why?

The solid — its particles are the most closely packed, so the most mass fits in a given volume.

True or false? The particles in a gas are larger than the particles in the same substance as a solid.

False. The particles are identical; in a gas they are simply much further apart.

What are the steps to determine the density of a regularly shaped solid?

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

1. Measure the dimensions with a ruler and calculate the volume: $2 \times 3 \times 5 = 30$ cm$^3$.
2. Measure the mass on a balance: $60$ g.
3. Density $= \dfrac{m}{V} = \dfrac{60}{30} = 2$ g/cm$^3$.

What are the steps to find the density of an irregular solid by displacement?

e.g. a small stone

1. Measure the mass of the stone on a balance.
2. Fill a displacement (eureka) can to the spout, lower the stone in on thin string and collect the displaced water in a measuring cylinder — this volume is the stone's volume.
3. Density $= \dfrac{\text{mass}}{\text{volume}}$.

What are the steps to measure the density of a liquid?

e.g. some cooking oil

1. Measure the mass of an empty measuring cylinder on a balance.
2. Pour in the liquid, record its volume, then measure the mass again and subtract to get the liquid's mass.
3. Density $= \dfrac{\text{mass of liquid}}{\text{volume of liquid}}$.

Which apparatus should be used to measure a small dimension, such as the diameter of a wire, more accurately than a ruler?

A micrometer or Vernier callipers.

Why should the measurements in a density experiment be repeated?

A mean can be calculated, which reduces the effect of random errors (and anomalies can be identified).

What are the names of the changes of state from solid to liquid and from liquid to solid?

Solid to liquid is melting; liquid to solid is freezing.

What are the names of the changes of state from liquid to gas and from gas to liquid?

Liquid to gas is boiling (or evaporating); gas to liquid is condensing.

What is sublimation?

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

What happens to the mass of a substance when it changes state?

The mass is conserved (stays the same) — no particles are created or destroyed.

Why is a change of state a physical change and not a chemical change?

No new substance is made — the material recovers its original properties if the change is reversed.

True or false? When water in a sealed container boils to form steam, the total mass decreases.

False. Mass is conserved in a change of state, so the total mass is unchanged.

True or false? When an irregular solid is fully submerged in a displacement can, the volume of water displaced is equal to the volume of the solid.

True. A fully submerged object pushes aside its own volume of water, which is collected and measured in a measuring cylinder.