SP14: Particle Model Flashcards
SP14a
1) Describe the arrangements of particles in solids, liquids and gases.
2) Use the particle model to explain the different properties of solids, liquids and gases.
3) Recall the formula relating density, mass and volume.
1) The kinetic theory states that everything is made of tiny particles.
In solids, forces of attraction hold particles closely together. The particles can vibrate but they cannot move around. This explains why solids keep their shape and usually cannot be compressed.
In liquids, the particles are moving faster and so the forces of attraction between the particles are not strong enough to hold them in fixed positions. The particles can move past each other so liquids flow and take the shape of their container. The particles are still very close together, so liquids usually can’t be compressed.
In a gas, the particles are far apart and moving around quickly. Gases are compressible and expand to fill their container.
2) The particle theory of matter is a model that describes the arrangement and movement of particles in a substance. The model is used to explain the physical properties of solids, liquids and gases.
3) Density is how much mass a substance has, per unit of its volume
Density (kg/m3) = mass (kg) / volume (m3)
SP14a
1) Use the particle model to explain why solids, liquids and gases have different densities.
2) Describe what happens to the mass of a substance when it changes state.
1) The density of a substance is the mass of a certain volume of the substance. Almost all substances are most dense when they are solids and least dense when they are gases. The arrangement of particles can explain the differences in density between different states of matter. A solid is usually denser than the same substance as a liquid, because the particles in solids are closer together.
2) With changes of state, mass is conserved. It does not change. These changes in state are called physical changes because the process can be reversed (eg. cooling instead of heating).
SP14b
1) Explain how heating affects the particles in a substance or object, including changes of state.
2) Describe how the temperature of an object changes with time while being heated or cooled to make it change state.
3) Define the term specific heat capacity.
1) It takes more energy to evaporate 1 kg of a substance than it does to melt 1 kg of the same substance, so these quantities are sometimes called the specific latent heats of melting and of evaporation. This energy is given out again when a substance freezes or condenses.
2) When enough energy is transferred to a solid by heating it reaches its melting point. If energy continues to be transferred, the temperature stops rising because the extra energy is used to overcome the forces between the particles and turn the solid into a liquid.
3) The specific heat capacity of a material is the amount of energy it takes to increase the temperature of 1 kilogram of the substance by 1°C.
SP14b
1) Define the term specific latent heat.
2) Explain the difference between specific heat capacity and specific latent heat.
3) Explain ways of reducing unwanted energy transfer through thermal insulation.
1) The amount of energy it takes to make 1 kg of a substance change state is called the specific latent heat.
2) Specific heat capacity is the energy needed to cause a temperature rise without causing a change of state, but specific latent heat is the energy needed to cause a change of state, where the temperature remains constant.
3) There are some simple ways to reduce this loss, including fitting carpets, curtains and draught excluders. Energy loss through windows can be reduced using double glazing. These kind of windows have air or a vacuum between the two panes of glass.
SP14c
1) Use the formula relating change in thermal energy, mass, temperature change and specific heat capacity. (You are given this formula)
2) Use the formula relating thermal energy, mass and specific latent heat. (You are given this formula)
3) What is the value of specific latent heat like when the substance changes state?
1) Change in thermal energy (J) = mass (kg) x specific heat capacity (J/kg degrees C) x change in temperature (degrees C)
2) Thermal energy needed for a change of state (J) = mass (kg) x specific latent heat (J/kg)
3) Energy is needed to make a substance melt or evaporate. The amount of energy depends on the mass of the substance and on its specific latent heat.
The value of specific latent heat for a substance is different for melting/solidifying and for evaporating/condensing.
SP14d
1) Explain how the movement of particles causes gas pressure.
2) Explain how changing the temperature of a gas affects the speed of its particles.
3) Explain how temperature affects the pressure of a fixed mass of gas at constant volume.
1) The gas pressure is caused by the gas particles continually moving and colliding with the walls of the container. This causes the particles to exert a force on on the walls of the container.
2) The particles in a gas are far apart from each other and move around quickly. The temperature of a gas is a measure of the average kinetic energy of the particles in the gas. The faster the average speed of the particles, the higher the temperature. Heating a gas increases the kinetic energy of the particles, so they move faster and the temperature rises. Increasing the temperature of a gas increases the speed of the particles, so it also increases the pressure of the gas.
2) The pressure of the gas increases when the temperature increases. This is because increasing the temperature of the gas increases the speed of the gas particles so they collide with the walls of the container more often and with more force.
SP14d
1) Explain the significance of absolute zero.
2) Convert temperatures between the Kelvin and Celsius temperature scales.
3) Explain the effects of different volumes of gas and the speed of gas on pressure
1) Absolute zero is the temperature at which particles stop moving or the temperature at which particles have the smallest amount of energy possible in their kinetic energy stores.
2) The kelvin temperature scale measures temperatures relative to absolute zero. The units are kelvin (K), and 1 K is the same temperature interval as 1 °C. Absolute zero is 0 K on this scale. To convert from kelvin to degrees Celsius, subtract 273.
To convert from degrees Celsius to kelvin, add 273.
The average kinetic energy of the particles in a gas is directly proportional to the kelvin temperature of the gas.
3) When the volume of gas is reduced, the pressure increases. When the volume of gas increases, the pressure is reduced.
The faster the particles are moving, the more frequent the collisions will be and the more force they will exert when they collide. Therefore, there will be a higher pressure.
SP14e
1) Explain how gases can be compressed or expanded by pressure changes.
2) Explain how the pressure of a gas produces a force at right angles to any surface.
3) Explain why changing the volume of a gas changes the pressure.
1) If you increase the pressure of a gas, it can be compressed. If you decrease the pressure of a gas, it can be expanded.
2) The effect of gas particles hitting a surface causes a net (overall) force on the surface. The force acts at right angles to the surface and we detect this as the gas pressure.
3) When the volume of the gas has decreased, the pressure increases because the particles are moving in less space and collide more often. When the volume of gas increases, the pressure decreases.
SP14e
1) Use the formula relating pressure and volume changes in a gas of fixed mass at constant temperature (this is given in the exam).
2) Explain why doing work on a gas can increase its temperature.
1) Starting pressure (P1) x starting volume (V1) = final pressure (P2) x final volume (V2)
P1 x V1 = P2 X V2
2) The gas exerts a pressure, and therefore a force on the object doing work (for example a bicycle pump). Work is done against this force when the object is pushed down. This transfers energy to the kinetic energy stores of the gas particles, increasing the average speed of the particles, which could increase the temperature of the gas.
SP14c - Core Practical
1) What is the aim of the investigating water core practical?
2) What is the method for the investigating water core practical?
1) Investigate the properties of water by determining the specific heat capacity of water and obtaining a temperature-time graph for melting ice.
2) Method Melting ice
Wear eye protection.
A Put a boiling tube full of crushed ice into a Pyrex [or heatproof] beaker. Put a thermometer in the ice and note the temperature.
B Put the beaker onto a tripod and gauze. Pour hot water from a kettle into the beaker, and keep it warm using a Bunsen burner.
C Measure the temperature of the ice every minute and record your results in a table. Stop taking readings three minutes after all the ice has melted.
D Note the times at which the ice starts to melt and when it appears to be completely melted.
Specific heat capacity
E Put a polystyrene cup in a beaker onto a battery-powered balance and zero the balance. Then fill the cup almost to the top with water and write down the mass of the water. Carefully remove the cup from the balance.
F Put a thermometer in the water and support it as shown in photo B.
Put a 12V electric immersion heater into the water, making sure the heating element is completely below the water level. Connect the immersion heater to a joulemeter.
G Record the temperature of the water, and then switch the immersion heater on. Stir the water in the cup gently using the thermometer.
H After five minutes record the temperature of the water again and also write down the reading on the joulemeter.
SP14c - Core Practical
1) What are the independent variable and dependent of the investigating densities core practical?
2) What are the risks of the core practical?
1) Independent Variable is the volume of the object. Dependent Variable is the mass of the object.
2) - Do not touch electrical equipment with wet hands
- Do not touch the heater, as it becomes very hot
- Switch the heater off when not in use and if it’s overheating
- When the thermometer is not being used, make sure it is placed where it cannot easily roll off the table.
SP14a - Core Practical
1) State possible sources of error in the experiment for the investigating densities core practical
2) Suggest why it is important that an object is completely submerged before you measure the volume of water displaced.
3) Explain why the density of a substance depends on its temperature
1) The measured mass was too low or the measured volume was too high. To improve the accuracy, use a measuring cylinder with more accurate markings. Zero the balance with the measuring cylinder on it and pour the liquid into that, so no liquid is left behind in the measuring cylinder.
2) To get an accurate value for the volume.
3) Changes in temperature can make a solid change volume (or increases/decreases in temperature make substances expand/ contract), and so the density must also change with temperature.
SP14a - Core Practical
1) What is the aim for the investigating densities core practical?
2) What is the method for the investigating densities core practical?
1) Investigate the densities of solids and liquids
2) Liquids
A. Put an empty beaker on a balance, and set the balance to zero.
B. Use a measuring cylinder to measure 50 cm3 of a liquid and then pour it into the beaker. Write down the reading on the balance. This is the mass of 50 cm3 of the liquid.
Solids
C. Find the mass of the solid and write it down.
D. Stand a displacement can on the bench with its spout over a bowl. Fill it with water until the water just starts to come out of the spout.
E. Hold a measuring cylinder under the spout and carefully drop your object into the can. If your object floats, carefully push it down until all of it is under the water. Your finger should not be in the water.
F. Stand the measuring cylinder on the bench and read the volume of water you have collected. This is the same as the volume of your object. Write it down.
