Unit 5: Solids, Liquids, Gases
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282 Terms
What happens to the energy transferred when a substance is heated?
It is stored as thermal energy within the system.
What are the two possible effects of heating a substance?
Increase temperature or cause a change of state.
What happens to particle kinetic energy when temperature increases?
It increases.
What happens to particle potential energy during a change of state?
It increases.
What happens to particle speed when temperature rises?
Particles move faster.
What happens to particle spacing during a change of state?
Particles become further apart.
What happens to temperature during melting or boiling?
It remains constant.
Why does temperature stay constant during melting or boiling?
The energy is used to overcome attractive forces between particles rather than increase kinetic energy.
What is melting?
The change of state from a solid to a liquid.
Is thermal energy absorbed or released during melting?
Absorbed.
What happens to particles during melting?
They vibrate more and overcome some attractive forces.
What happens to temperature while a solid is melting?
It stays constant until all the solid has melted.
What is boiling?
The rapid change of state from a liquid to a gas throughout the liquid.
Where does boiling occur?
Throughout the liquid.
Does boiling happen at a fixed temperature?
Yes, at the boiling point.
What forms throughout a liquid during boiling?
Bubbles.
What happens to temperature during boiling?
It remains constant.
What is evaporation?
The change of state from a liquid to a gas at the surface only.
Where does evaporation occur?
At the surface only.
Can evaporation happen at any temperature?
Yes.
Which particles escape during evaporation?
The fastest-moving particles.
Why does evaporation cause cooling?
The highest-energy particles leave first, reducing the average kinetic energy of the remaining particles.
What are the three differences between boiling and evaporation?
Boiling happens throughout the liquid at a fixed boiling point with bubbles; evaporation happens at the surface at any temperature without bubbles.
How are particles arranged in a solid?
Closely packed in a regular arrangement.
How do particles move in a solid?
They vibrate about fixed positions.
How are particles arranged in a liquid?
Close together in a random arrangement.
How do particles move in a liquid?
They move past one another.
How are particles arranged in a gas?
Far apart in a random arrangement.
How do particles move in a gas?
Rapidly in all directions.
Which state has the lowest particle energy?
Solid.
Which state has medium particle energy?
Liquid.
Which state has the highest particle energy?
Gas.
Which state has a fixed shape and fixed volume?
Solid.
Which state has a fixed volume but takes the shape of its container?
Liquid.
Which state fills its container and has no fixed volume?
Gas.
What happens to particles during melting?
They gain energy, vibrate more, overcome some attractive forces and begin moving past each other.
What happens to particles during boiling?
They gain enough energy to completely overcome attractive forces and escape as a gas.
What does a sloping line on a heating curve show?
Temperature is increasing.
What does a flat line on a heating curve show?
A change of state is occurring.
Why is a heating curve horizontal during melting or boiling?
Thermal energy is used to overcome attractive forces, so kinetic energy and temperature do not increase.
What is specific heat capacity?
The energy required to raise the temperature of 1 kg of a substance by 1°C.
What is the unit of specific heat capacity?
J/kg°C.
What does a high specific heat capacity mean?
More energy is needed to raise the temperature.
Why does water heat up slowly?
It has a high specific heat capacity.
Why do metals usually heat up quickly?
They have lower specific heat capacities.
What is the specific heat capacity equation?
ΔQ = mcΔT.
What does ΔQ represent?
Change in thermal energy (J).
What does m represent?
Mass (kg).
What does c represent?
Specific heat capacity (J/kg°C).
What does ΔT represent?
Temperature change (°C).
How do you calculate mass from the SHC equation?
m = ΔQ ÷ (cΔT).
How do you calculate specific heat capacity?
c = ΔQ ÷ (mΔT).
How do you calculate temperature change from the SHC equation?
ΔT = ΔQ ÷ (mc).
How do you calculate temperature change?
Final temperature − Initial temperature.
A substance heats from 20°C to 65°C. What is the temperature change?
45°C.
A 2 kg block receives 3600 J and has a specific heat capacity of 400 J/kg°C. What is the temperature increase?
4.5°C.
What apparatus is needed for the SHC practical?
Metal block or water, immersion heater, thermometer, power supply, balance, stopwatch and insulation.
What is the first step in the SHC practical?
Measure the mass.
What temperatures should be recorded in the SHC practical?
Initial and final temperatures.
How is specific heat capacity calculated in the practical?
c = ΔQ ÷ (mΔT).
What is the independent variable in the SHC practical?
The material used.
What is the dependent variable in the SHC practical?
Temperature change.
Give three control variables for the SHC practical.
Mass, heater power and heating time.
How can heat loss be reduced in the SHC practical?
Insulate the block.
Why should the thermometer be fully inserted?
To measure the temperature accurately.
Why should water be stirred gently during the practical?
To ensure an even temperature.
When should timing begin in the SHC practical?
As heating begins.
What happens during heating without a change of state?
Kinetic energy increases and temperature rises.
What happens during heating with a change of state?
Potential energy increases and temperature stays constant.
What is a common exam trap about boiling and evaporation?
They are different processes.
What is the key difference between boiling and evaporation?
Evaporation happens only at the surface and at any temperature.
Does temperature rise during melting or boiling?
No, it stays constant.
What should the heating curve look like during a change of state?
A horizontal flat line.
Should you use final temperature or temperature change in SHC calculations?
Temperature change.
What is the correct formula for temperature change?
ΔT = Final − Initial.
What is the correct unit for specific heat capacity?
J/kg°C.
What is the key idea of the kinetic model of gases?
A gas is made of tiny molecules moving in constant random motion.
How do gas molecules move?
In constant random motion in all directions.
Why do gases produce pressure?
Gas molecules collide with the walls of their container.
What causes pressure in a gas?
Molecules colliding with the walls of their container.
What happens during each collision between a gas molecule and the container wall?
It exerts a force on the wall.
Why do many molecular collisions create pressure?
The combined forces of many collisions produce pressure.
What is the exam definition of pressure in a gas?
Pressure is caused by molecules colliding with the walls of their container.
What is absolute zero?
The lowest possible temperature.
What is absolute zero in Celsius?
−273°C.
What is absolute zero in Kelvin?
0 K.
What happens to molecular kinetic energy at absolute zero?
It is at its minimum possible value.
What happens to the average speed of molecules at absolute zero?
It is as low as possible.
Can temperature go below 0 K?
No.
What is the exam definition of absolute zero?
The temperature at which particles have minimum kinetic energy.
What is the SI unit of temperature?
Kelvin (K).
Why does the Kelvin scale never have negative values?
It starts at absolute zero.
Where does the Kelvin scale begin?
0 K (absolute zero).
How do you convert Celsius to Kelvin?
K = °C + 273.
How do you convert Kelvin to Celsius?
°C = K − 273.
What is 0°C in Kelvin?
273 K.
What is 25°C in Kelvin?
298 K.
What is 100°C in Kelvin?
373 K.
What is −273°C in Kelvin?
0 K.
What must you do before using gas equations with temperature?
Convert Celsius to Kelvin.