Particle Model Flashcards
Explain the densities of solids, liquids and gases?
Solids and liquids have similar densities. This is because the space between particles does not change significantly. Usually, liquids have a lower density than solids (the main exception is ice and water).
Gases have a far lower density. The spacing between atoms increases as the particles have lots of energy to move, so volume increases greatly and therefore density decreases.
Describe the changes of state
Deposition: gas to solid
Sublimation: solid to gas
Melting: solid to liquid
Freezing: liquid to solid
Evaporation: liquid to gas
Condensation: gas to liquid
These are physical changes as the material retains its original properties when reversed.
CORE PRACTICAL - Investigate the densities of solid and liquids
Measure density of solids
1. Weigh regular and irregular solids using a zeroed balance.
2. For regular solids, use appropriate measurements to find the volume.
3. For irregular solids, fill up a displacement can until water comes pouring out the nozzle. To prevent water form going on the floor, place a beaker to catch the water and then when water stops dropping empty the beaker for next step and place the empty beaker under the nozzle.
For solids that float, you can either push the solid down into the water, until it is fully submerged, or you can weigh it down with something of a known volume and subtract that value by the solid in the water – this is more accurate.
4. Place the solid into the displacement can and wait for all the water to pour out the nozzle into the beaker. When all water has come out, pour water into a measuring cylinder and record the volume at the meniscus (lowest point of the water-the centre).
5. Using the mass and the volume you can calculate the density using the equation density = mass/volume.
Measuring density of liquids
1. Place empty measuring cylinder on balance, and zero it. Fill measuring cylinder and take the reading of any volume with water and measure the mass.
2. Use the equation density = mass/volume
Explain how heating a system will change the energy stored within the system
It raises its temperature or produce changes of state.
The amount of energy the particles have increases and particles vibrate more.
Define the term specific heat capacity
The energy required to raise the temperature of 1kg of a substance by 1-degree Celsius.
Define the term specific latent heat
The energy to change the state of 1kg of a substance without a change in temperature.
Explain ways of reducing unwanted energy transfer through thermal insulation
Thermal energy transfers out of any system. This means some energy is wasted, and, as it is lost to the surroundings.
Using a thermal insulator, e.g., foam, reduces the amount of energy lost as it’s a poor thermal conductor.
Use reflective coatings to reflect IR radiation (heat) back into the system.
CORE PRACTICAL - Investigate the properties of water by determining the specific heat capacity and obtaining a temperature-time graph for melting ice
Part 1: Obtaining a temperature-time graph for melting ice
1. Fill the beaker with boiling water and maintain its temperature using a Bunsen burner, ensuring stability with a thermometer.
2. Fill a boiling tube, with crushed ice and record the initial temperature.
3. Place the boiling tube in the beaker and start the stopwatch.
4. Record ice temperature every 30 seconds until all the ice has melted Take note of the state of the ice (or liquid), for every recorded temperature.
5. Plot a graph of temperature against time, emphasizing the plateau during ice melting, indicating energy going into breaking water atom bonds instead of temperature increase.
Part 2: Determining the specific heat capacity of water
1. Zero an empty beaker on the balance.
2. Fill the beaker with water and record its mass.
3. Insert a thermometer and immersion heater in the water and insulate the beaker with cladding (ensure the top is also covered with a lid). The immersion heater should also be connected to a joulemeter to measure the energy transferred during heating.
4. Record the initial water temperature and turn on the immersion heater.
5. Let the heater heat the water for an hour, or until there is a significant change in temperature, and then take the final temperature reading as well as recording the value on the joulemeter. Using a electric stirrer the water should be continually stirred so the heat is evenly distributed.
6. Using the formula
Specific heat capacity = Energy/(mass x change in temperature)
Explain the pressure of a gas in terms of the motion of its particles
Particles in a gas move randomly in every direction.
Remember, pressure produces a net force at right angles to any surface. Particles collide with a wall, changing velocity. This means they change momentum during their collision, so they exert a force on the wall.
Explain the effect of changing the temperature of a gas on the velocity of its particles
Increased temperature means more energy given to the particles and they move at faster speed. The thermal energy is transferred to kinetic energy. Collisions with walls occur often and the particles also hit the wall with greater impact and so pressure increases.
Describe the term absolute zero
This temperature is 0 kelvin or –273 degrees Celsius.
Nothing can exist at a colder temperature than this, this is the coldest temperature possible.
Particles at this temperature have no energy so they don’t vibrate at all, they remain still.
Explain that gases can be compressed or expanded by pressure changes
Gases want to remain at a constant temperature.
Increasing the pressure of the gas causes it to compress and have a smaller volume. Pressure increases so greater force per area. The same force is exerted on walls, as temperature and energy of particles is constant. Force needs to be exerted on a smaller area and volume decreases.
When volume increases, there is greater area particles collide with. Same force is exerted on the walls as velocity is constant and pressure decreases.
Explain the effect of changing the volume of a gas?
Doing work on a gas means compressing or expanding the gas, so changing the volume. Pumping more gas into the same volume means more particles are present, so more collisions occur per unit time with the walls so pressure increases. Energy is transferred to the particles when more gas is added into the fixed volume, so this heats the gas.
