Solids, liquids and gases flashcards

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What is density? Give the equation and units.
Density is mass per unit volume: ρ = m ÷ V. ρ is in kg/m³ (or g/cm³), m in kg (or g), V in m³ (or cm³).
A block has mass 240 g and volume 30 cm³. What is its density?
ρ = m ÷ V = 240 ÷ 30 = 8.0 g/cm³ (which is 8000 kg/m³).
How can you find the density of an irregular solid?
Measure its mass with a balance. Find its volume by displacement: submerge it in a eureka can or measuring cylinder and measure the water displaced. Then ρ = m ÷ V.
How can you find the density of a liquid?
Place a measuring cylinder on a balance and zero it. Add a known volume of liquid and read the mass. Then ρ = m ÷ V.
(Paper 2) Compare the arrangement and movement of particles in solids, liquids and gases.
Solids: closely packed in a regular pattern, vibrating. Liquids: close but irregular, able to flow past each other. Gases: far apart, moving randomly and fast.
Why are gases much less dense than solids and liquids?
Gas particles are far apart, so there is very little mass in a given volume. Solid and liquid particles are almost touching.
(Paper 2) What happens to the particles during melting and boiling?
Energy supplied breaks the bonds between particles. The temperature stays constant during the change of state while internal energy increases.
(Paper 2) What is internal energy?
The total of the kinetic and potential energies of all the particles in a system. Heating increases the particles' kinetic energy, or their potential energy during a change of state.
How does the kinetic model explain gas pressure?
Gas particles move randomly and collide with the container walls. Each collision exerts a tiny force; the many collisions per second give a steady pressure on the walls.
How does temperature relate to the motion of gas particles?
Higher temperature means a higher average kinetic energy, so the particles move faster. Their collisions with the walls are harder and more frequent, so pressure rises.
(Paper 2) What is the specific heat capacity of a substance?
The energy needed to raise the temperature of 1 kg of the substance by 1 °C. It is measured in J/kg °C.
(Paper 2) State the equation linking energy, mass, specific heat capacity and temperature change.
ΔQ = m c Δθ. ΔQ is thermal energy in J, m is mass in kg, c is specific heat capacity in J/kg °C and Δθ is temperature change in °C.
(Paper 2) How much energy heats 2.0 kg of water by 15 °C? (c = 4200 J/kg °C)
ΔQ = mcΔθ = 2.0 × 4200 × 15 = 126 000 J (126 kJ).
(Paper 2) Describe an experiment to find the specific heat capacity of a metal block.
Fit a heater and thermometer in the insulated block. Record voltage, current, time and the temperature rise. Use E = VIt = mcΔθ, so c = VIt ÷ (mΔθ). Insulate to reduce heat loss.
(Paper 2) Describe the temperature–time graph as ice is heated until it becomes steam.
The graph rises as the solid warms, is flat while it melts, rises as the liquid warms, is flat while it boils, then rises as the gas warms. During the flat sections the energy supplied changes the arrangement of particles, not their temperature.
How does pressure act at a point in a fluid at rest?
Equally in all directions. At the same depth in the same liquid the pressure is the same everywhere, whatever the direction or shape of the container.
How is the kelvin temperature of a gas linked to its particles?
It is proportional to the average kinetic energy of the particles. Doubling the kelvin temperature doubles their average kinetic energy; at 0 K they have minimum kinetic energy.
How can you find the density of a regularly shaped solid such as a cuboid?
Measure its mass on a balance. Measure length, width and height with a ruler or calipers and multiply to find the volume. Then ρ = m ÷ V.
What is pressure? State the equation and unit.
Pressure is force per unit area: p = F ÷ A. The unit is the pascal (Pa), equal to 1 N/m².
A force of 600 N acts on an area of 0.020 m². What is the pressure?
p = F ÷ A = 600 ÷ 0.020 = 30 000 Pa.
Why do sharp knives and skis demonstrate pressure differences?
A knife has a small area so the same force gives a large pressure, which cuts easily. Skis spread weight over a large area, giving a small pressure so they do not sink.
How does pressure in a liquid depend on depth and density?
Pressure increases with depth and with density: p = h × ρ × g. h is depth in m, ρ is density in kg/m³ and g is 9.8 N/kg.
Find the pressure due to water 2.0 m deep (ρ = 1000 kg/m³, g = 9.8 N/kg).
p = hρg = 2.0 × 1000 × 9.8 = 19 600 Pa.
What is absolute zero and what is it on the Celsius scale?
The lowest possible temperature, where particles have minimum kinetic energy. It is 0 K, which is −273 °C.
How do you convert between Celsius and kelvin?
T (K) = θ (°C) + 273. For example 27 °C = 300 K. Gas law calculations must use kelvin.
What is the relationship between the pressure and volume of a gas at constant temperature?
Pressure is inversely proportional to volume, so pV is constant: p₁V₁ = p₂V₂ (Boyle's law). Squeezing the gas into less space means more collisions per second with the walls.
A gas at 100 kPa is compressed from 6.0 cm³ to 2.0 cm³ at constant temperature. Find the new pressure.
p₂ = p₁V₁ ÷ V₂ = 100 × 6.0 ÷ 2.0 = 300 kPa.
What is the relationship between pressure and temperature for a gas at constant volume?
Pressure is directly proportional to absolute temperature: p₁ ÷ T₁ = p₂ ÷ T₂, with T in kelvin. Hotter particles hit the walls harder and more often.
A gas at 100 kPa and 300 K is heated to 330 K at constant volume. Find the new pressure.
p₂ = p₁ × T₂ ÷ T₁ = 100 × 330 ÷ 300 = 110 kPa.

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