14. Particle Model Flashcards
What is the definition of density? State the unit.
The mass per unit volume of a material.
Unit: kg/m³
What is meant by a state of matter?
A form in which matter can exist, based on the particle arrangement in a substance.
Give the different states of matter in order of increasing density of atoms (lowest to highest).
least —> most
gas, liquid, solid
Use kinetic theory to explain the structure of liquids.
The particles have some kinetic energy. They are free to move and can move around in random directions at very slow speeds.
Explain the movement of particles in a solid.
The particles vibrate around a fixed position as they do not have enough kinetic energy to move freely.
Describe the structure of particles in a gas.
Particles in a gas have almost no forces between them therefore they are completely free to move, and move at high speeds in random directions.
What is always conserved when a substance undergoes a change of state?
Mass
How does a change of state differ from a chemical change?
In a change of state, the material can return to having its previous properties if the change is reversed.
What is the internal energy of a substance?
- The energy stored by the particles.
- The sum of the total kinetic and potential energies that make up the system.
What two things can heating a substance do?
- Raise its temperature.
- Change the state of the substance.
What three factors determine the temperature change of a system?
- Mass of substance being heated.
- Type of material (specific heat capacity)
- Energy inputted into the system.
What is sublimation?
When a solid turns directly into a gas.
What is the difference between physical changes and chemical changes in substances?
Physical changes can be reversed, chemically changes cannot be easily reversed.
How does heating cause a substance to change state?
Heating matter gives particles more potential energy. This energy is used to break the bonds of attraction, leading to a change of state.
Why does heating increase the temperature of a substance?
It increases the amount of thermal energy in that substance. It also gives the particles more kinetic energy, meaning they move faster and their temperature increases.
Define specific heat capacity.
The amount of energy needed to increase the temperature of 1kg of a substance by 1⁰C.
Define specific latent heat.
The amount of energy needed to change the state of 1kg of a substance with no change in temperature.
Explain the pressure of a gas in terms of the motion of particles.
The particles move in random directions. When they collide with the walls of a container they exert a force which acts at a right angle to the container. This causes pressure.
What factor affects the average kinetic energy of gas molecules?
- The temperature of the gas.
- The higher the temperature, the higher the average kinetic energy of the molecules.
What effect does increasing temperature have on the pressure of a gas when held at constant volume?
Gas pressure will increase as the temperature increases.
Why does pressure increase as temperature increases (at a constant volume)?
- Kinetic energy of molecules increases.
- Collisions between molecules becomes more frequent.
- Greater rate of change of momentum.
- Greater force and therefore pressure.
If gas A is at a low pressure, and gas B is at a high pressure, what can be said about the rate of collisions in each gas?
- There are more collisions per second in gas A than in gas B.
- The rate of collisions is higher in A.
Explain how increasing the volume of a gas results in a decrease of pressure.
- Molecules become more spread out so rate of collision decreases.
- Rate of change of momentum decreases, and so force exerted on container decreases, resulting in a lower pressure.
What is the unit used for pressure?
Pascal (Pa)
How do you convert between degree celsius and kelvin?
Kelvin (K) to degrees celsius (⁰C) = +273
Degrees celsius (⁰C) to kelvin (K) = -273
What is absolute zero?
-273⁰C
Particles have no kinetic energy and do not move.
