Topic 14 - Particle Model Flashcards
Paper 1
What is Density?
+Mass per unit volume
+Density is a measure of the “compactness” of a substance.
+it relates to the mass of a substance to how much space it takes up.
+The symbol for density is a Greek letter rho [p] - it looks like a p but it isn’t.
What is the equation for density?
What does the density of an object depend on?
+What it’s made of.
+Density doesn’t vary with size or shape.
What does the average density of an object determine?
+Whether it floats or sinks - a solid object will float on a fluid if it has a lower average density than the fluid.
How do you find the density of any substance?
+Measure its mass and volume and use the formula
What is the easiest process of finding the density of a liquid?
- +Use a measuring cyclinder
- Use a mass balance to meassure the mass of the empty measuring cyclinder.
- Pour in the liquid to be investigated & measure the mass of the cyclinder again - the difference in mass is equal to the mass of the liquid.
- Finding the volume of the liquid involves reading from the cylinder’s scale [1ml=1cm3]
- [Measuring the volume of a prism involves finding the area of the base then multiplying by height.
What happens when you want to find the volume of an irregular shape?
+You can find its volume using the fact that an object submerged in water will displace a volume of water equal to its own volume.
+You can do this using a density bottle
What is the process of using a density bottle to find the volume of an irregular shape?
1. Measure the mass [m1] of the object using a mass balance
- Fill the bottle with a liquid of a known density [eg. water]
- Place the stopper into the bottle and dry the outside
- Measure the mass of the bottle [m2]
- Empty the bottle and place the object into the density bottle [repeat steps 2 and 3] - measure the mass of the bottle [m3]
- Calculate the volume of displaced water: -
- The mass of the displaced water = m2 - [m3 - m1]
- Density of water is 1g/cm3 so you can use V=m/p to find the volume displaced - this equals the volume of the object.
- Calculate the density of the object using p=m/v with the mass you measured in step 1 [m1] and the volume calcualted in step 6.
What can you also use if you don’t have access to density bottles?
+ A eureka can and a measuring cylinder
+This is a density bottle
What are some common densities?
What is Kinetic Theory?
+The particles that make up matter are tiny balls
+You can explain the way that matter behaves in terms of how these tiny balls move, and the forces between them.
What are the three states of matter?
- Solid [eg. ice]
- Liquid [eg. water]
- Gas [eg. water vapour]
+The particles of a substance in each state are the same - only the arrangement and energy of the particles are different.
+If you reverse a change of state, the particles go back to how they were before.
What are changes of state?
+Physical changes [only the form of a substance changes]
+These are different from chemical reactions, where new substances are created by the reaction.
What happens when a change of state occurs?
+When a change of state occurs, the spacing brtween particles changes, so internal energy of the substance also changes.
+As the paticles get closer together, their internal energy decreases.
What happens in solids?
+Strong forces of attraction hold the particles close together in a fixed, regular arrangement.
+The particles don’t have much energy in their kinetic energy stores so they can only vibrate about their fixed positions.
What happens in liquids?
+The forces of attraction between the particles are weaker - the particles are close together, but can move past each other and form irregular arrangements.
+They have more energy in their kinetic energy stores than the particles in a solid - they move in random directions at low speeds.
What happens in gases?
+There are almost no forces of attraction between the particles
+Particles have more energy in their kinetic energy stores than those in liquids and are free to move - they travel in random directions at high speeds.
How do you get from a solid to a liquid?
Melting
How do you get from a liquid to a solid?
Freezing
How do you get from a liquid to a gas?
Evaporation
How do you get from a gas to a liquid?
Condensation
How do you get from a gas to a solid?
Sublimation
How do you get from a solid to a gas?
Sublimation
How is the energy in a substance’s thermal energy store held?
+By its particles in their kinteic energy stores - this is what the thermal energy store actually is.
What happens when you heat a liquid?
+The extra energy is transferred into the particles’ kinetic energy stores, making them move faster.
+Eventually, when enough of the particles have enough energy to overcome their attraction to each other, big bubbles of gas form in the liquid - this is boiling.
What happens when you heat a solid?
The extra energy makes the particles vibrate faster until eventually the intermolecular forces between them are partly overcome and the particles start to move around - this is melting.
What varies with state and what doesn’t?
Density of a substance varies with state but mass doesn’t.
What isn’t affected when a substance changes state?
+Provided you’re working with a closed system [ie. no particles can escape, and no new particles can get in] the mass of a substance isn’t affected when it changes state.
+This is because the mass of a substance is the mass of its particles - and the particles aren’t changing, they’re just being rearranged.
When does volume change?
+When a substance changes state.
+The particles in most substances are closer together when they’re a solid than a liquid [except ice and water], and are closer together when they’re a liquid than a gas.
+Since density = mass/volume, then density must change too. Generally, substances are most dense when they’re solids and least dense when they’re gases.
What does specific heat capacity relate?
Temperature and energy
What does heating a substance do?
+Increases the energy in its thermal energy store [or the kinetic energy stores of its particles] - can also be referred to as internal energy of a substance.
In kinetic theory, what is temperature?
+A way of measuring the average internal energy of a substance
+For some materials, what does it take more of to increase its temperature?
+It takes more energy to increase the temperature of some materials than others
+Eg. you need 4200J to warm 1kg of water by 1oC but only 139J to warm 1kg of mercury by 1oC
What is the specific heat capacity equation?
Give the diagram of the specific heat capacity experiment.
What is the experiment for the temperature of changes of state?
- Fill a beaker with crushed ice.
- Place a thermometer into the beaker and record the temperature of the ice.
- Every twenty seconds, record the temperature and the current state of the ice [eg. partially melted, completely melted].
- Continue this process until the water begins to boil.
- Plot a graph of temperature against time for your experiment - it should look like the graph for heating a substance.
What does the graph for heating a substance look like?
What does the graph for cooling a substance look like?
What is the equation for specific latent heat?
+You can work out the energy needed [or released] when a substance of mass m changes state using this formula:
What is the relationship for a gas of fixed mass at a constant temperature?
Give a table of the kelvin scale and celsius scale
Why does a gas exert a force on its container?
+Due to collisions between the particles and the walls of the container.
+These collisions happen in random directions, but add together to produce a net [overall] force at right angles to the wall of the container.
What is the process of changing the pressure of a gas inside a non-fixed volume container [eg. a balloon] by heating or cooling?
- As the baloon is heated, the gas particles inside it gain energy and move around quicker - this increases the pressure of the gas inside a balloon.
- The outwards pressure of the gas inside the balloon is now larger than the inward pressure by the surroundings - the balloon [and so the volume of the gas] expands until the pressures are equal once more.
- Cooling the gas in the balloon has the opposite effect - the outward pressure is smaller than the inward pressure, so the gas inside the balloon is compressed.
Describe the process of changing the external pressure on a gas.
+You can change the external pressure of a gas in a number of ways:
- For a gas in an airtight syringe, pushing hard on the plunger increases the inward pressure on the gas, so that it is larger than the outward pressure - this causes the gas of the syringe to be compressed.
- Atmospheric pressure decreases as altitude increases, so as a container of a gas rises, the inward pressure decreases - this causes the gas to expand as the altitude increases.
