Chapter 6: Molecules and Matter Density. States of Matter and Internal Energy. Changes of State. Specific Latent Heat. Gas pressure and temperature. Gas pressure and volume.

Density

C has the greatest mass per volume. Density, Volume & Mass A B C Which volume of particles do you think will have the greatest mass? C, as it has the greatest amount of particles in the fixed volume it will have the greatest mass compared to A & B C has the greatest mass per volume.

Equation for Density Calculate the density of? mass (kg) ‘ρ’ is the a greek letter we use for density, we do not use ‘d’   density (kg/m3) What are the units for density? volume (m3) mass per volume Calculate the density of?   Given a material has a density of 200 kg/m3 and you have 5 m3 of it. What mass of the material do you have?

Density of regular objects. For each object measure the: - Length - Width - Height Length (m) Width (m) Height (m) Volume (m3) Mass (kg) Density(kg/m3) REQUIRED PRACTICAL 5

Density of irregular objects (by ‘displacement technique’) Like Archimedes we can use water. Measure the mass of the object with the scales. Fill a displacement can with water. Carefully place the object in the water and collect the water that is displaced using a measuring cylinder. Record the volume of displaced water and use this to calculate the density of your object. 1 ml = 1 cm3 = 0.000001 m3 REQUIRED PRACTICAL 5

Density of liquids Place measuring cylinder on balance and zero balance. Pour 10ml of the liquid into cylinder and record mass. Add additional 10ml volumes and each time record the mass. Calculate the density for each measurement. Take an average of each of these values. Volume (ml) Mass (g) Density (g/cm3) 10 20 30 40 50 Ave. density (g/cm3) REQUIRED PRACTICAL 5

States of Matter and Internal Energy.

STARTER Draw a particle diagram to represent the 3 different states of matter. C C C SOLID LIQUID GAS REGULAR PATTERN FIXED POSITION VIBRATE ON SPOT KEEP THEIR SHAPE RANDOM ARRANGEMENT CLOSE TOGETHER MOVE AROUND TAKE SHAPE OF CONTAINER RANDOM ARRANGEMENT FAR APART MOVE IN ALL DIRECTIONS FILL A VOLUME What other properties of these different states can you state?

Kinetic theory of matter - SOLIDS Particles in a solid are held together by strong forces of attraction and vibrate about their position. At low temperatures the vibration is small and can be considered fixed. When a solid gains energy the particles vibrate more and cause the neighbouring particles to vibrate also. C )( )( )( )( )( )( )( Can be thought of as atoms bound together by springs. Given energy they will all vibrate about their position passing energy on, with the external energy source removed all the atoms will return to their original position. )( )( )( )( )( )( )( )( )( )( )( )( )( )( )( )(

Kinetic theory of matter - LIQUIDS The intermolecular forces within a liquid are too weak to keep particles in a fixed position and so are free to move. They move randomly and so therefore liquids flow.

Kinetic theory of matter - GASES The particles in a gas are in constant random motion as there are very weak forces between them. The particles are spaced further apart than in liquids.

So what is this energy and what is it from? Already moving…. The particles of a substance in each different state of matter are already moving – even before we start heating it. So what is this energy and what is it from? The particles in a substance have energy, this is called ‘internal energy’ – this relates to the particles motion and position.

Internal Energy What is it? The kinetic energy they have due to motion of individual particles. The potential energy the particles have due to their position. Particles gif - http://ozonedepletiontheory.info/ImagePages/translational-kinetic-energy.html Particles moving gif - http://wiki.chemprime.chemeddl.org/index.php?title=File:Gassim.gif&limit=50 The internal energy of a substance is the combined energy of the kinetic and potential energy of the particles in the substance (or system).

Potential energy and state What happens if the position of the particles in a substance changes? It changes state as the potential energy of the particles increases and therefore the overall internal energy increases. We can cause substances to change state by increasing their internal energy or lowering their total internal energy. In order to change state by changing the positions of particles in a substance there must be a change of energy in relation to the forces between particles. The energy to cause a change in state of a substance is referred to as the ‘latent heat.’

Increasing internal energy What happens when you increase the overall internal energy of a substance? Heating the substance will increase the particles kinetic energy and therefore the overall internal energy. This will cause an increase in temperature. 2. A change in state causes a change in the potential energy of the particles, therefore the overall internal energy. Flame - https://pixabay.com/en/fire-hot-flame-power-heat-danger-305340/ Beaker - https://pixabay.com/en/beaker-experiment-bubbles-chemistry-148167/

Changes of State and Specific Latent Heat.

Changing states of matter Label each part of graph to show the state of matter at each point – 1, 2 & 3. Evaporating GAS Temperature Melting LIQUID Condensing SOLID Freezing Time Why is this line straight?

Experiment – Changes in state At the melting point, the temperature stops rising while the solid melts.. If a solid is heated, its temperature rises until it reaches the melting point of the solid. Evaporating GAS Temperature Melting LIQUID SOLID This is because heat energy is going into separating the particles rather than raising the temperature Time

Latent heat of fusion ‘Specific latent heat of fusion’ refers to the energy supplied to change 1kg of a substance from solid state to liquid state. So how much energy does it take? For example how much energy to melt ice

Equation for Latent heat of fusion Energy (J)   Specific latent heat of fusion (J/kg) Mass (kg) Calculate the specific latent heat of fusion for water/ice since 2 kg of ice requires 668 kJ of energy to melt.   Calculate the specific latent heat of fusion for mercury. 2.5 kg of mercury requires 27.5 kJ of energy to melt it.  

Latent heat of vaporisation ‘Specific latent heat of vaporisation’ refers to the energy supplied to change 1kg of a substance from liquid state to gaseous state.

Gas Pressure

Kinetic Theory of Matter The Kinetic Theory of Matter states that matter is composed of a large number of small particles (individual atoms or molecules) that are in constant motion. Average kinetic energy of particles/molecules Average spacing of particles/molecules

“Brownian Motion” How do we know this? Demonstrate Brownian Motion with smoke cell or alternatively use video. https://www.youtube.com/watch?v=ygiCHALySmM “Brownian Motion”

Boardworks Science The particle model

What is Pressure? Pressure refers to when a continuous force is exerted onto a surface. Therefore pressure can be thought of as force per unit area (per m2). Molecules continuously colliding with a surface and exerting a force on that surface therefore cause pressure to be exerted by a gas.

How does temperature effect pressure? The higher the temperature the greater the kinetic energy of the particles. This means they travel with greater speed. Frequency of collisions increased and force exerted as they collide. Pressure goes up.

How are pressure and volume are related? What would happen the volume of fluid in a container if the pressure was increased? What would happen to the pressure of fluid in a container if the volume was increased?

Pressure and Volume For a fixed mass of gas that has it’s volume or pressure changed the number of molecules remains constant. Also provided the temperature remains constant so will the average speed of the molecules. 1 2 Why does the pressure increase if the volume is reduced for a fixed amount of gas? Due to having a smaller volume (space) the molecules collide more frequently with the internal surface, increasing the total force per unit area.

Relationships - Boyle’s Law P x V = constant There is an inversely proportional relationship between pressure and volume   As the pressure increases the volume decreases. As the volume increases the pressure decreases

Boyle’s Law: Key points