Pg. 169 171, 173-175 Syllabus 5.7 5.14 www.cgrahamphysics.com
What do you remember? End www.cgrahamphysics.com
How do particles move? 3 of 30 Boardworks Ltd 2012
4 of 30 Boardworks Ltd 2012 States of matter Solid Fixed shape and Volume Particles held together in bonds They can only vibrate Particles arranged in regular pattern Very dense, cannot be compressed Liquid Fixed volume, but can flow to take any shape Particles are close together, but have no regular pattern They can slide over each other Not as dense as solids Cannot be compressed easily
5 of 30 Boardworks Ltd 2012 Gas No fixed shape or volume Particles motion is rapid and random They are spread out They collide with each other and the sides of the container Not dense, can easily be compressed How do we know? Brownian Motion Brownian Motion - YouTube [360p].mp4 Big smoke particles are moved by much smaller air particles, which are too small to be observed Big massive smoke particles are moved by light, fast moving air particles
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} Particles in solids, liquids and gases have KE because they are moving } Internal energy is the sum of PE and KE of all molecules } They also have PE because their motion keeps them separated and opposes the bonds trying to pull them together } Energy transfer from hot to cold is heat Internal energy Heat www.cgrahamphysics.com
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Particles 9 of 30 Boardworks Ltd 2012 What happens to the kinetic energy of the particles when a gas is heated? Temperature= average KE of particles The heat energy is transferred to the kinetic energy of the gas particles. The KE of the particles increases. This means that the particles start moving faster What sort of graph would you get if you plotted Kelvin temperature (T k ) against the average kinetic energy (KE ave )of the particles. KE ave Zero Kelvin temperature equals zero gas molecule kinetic energy. T k At what temperature is zero Kelvin? -273 C
Kelvin and Celcius scales 10 of 30 Boardworks Ltd 2012 The Celsius scale is defined using the freezing and boiling points of water. This makes it less useful for calculations, because 0 C is not at the beginning of the scale. 273 200 100 0 100 200 300 400 500 Celcius ( C) 0 73 173 473 673 273 373 573 773 Kelvin (K) Using the Celsius scale for temperature is like measuring mass on a scale that takes 273 kg as zero mass and measures anything less than that as negative mass! The Kelvin scale starts from absolute zero ( 273 C). A difference in temperature of 1 K is the same as a difference of 1 C, so it is easy to convert between the two scales.
C 11 of 30 Boardworks Ltd 2012 Kelvin temperature (K) 273K -273 C Celsius temperature ( C) T k = T c + 273K
Converting temperatures 12 of 30 Boardworks Ltd 2012 Celsius temperature ( C) 0 Kelvin temperature 273 (K) 27-226 183 483 300 47 456 756
Gas pressure 13 of 30 Boardworks Ltd 2012
Pressure and particles 14 of 30 Boardworks Ltd 2012 What causes pressure in gases? In a sealed container, the particles repeatedly strike the walls of the container. This causes pressure. What happens if you increase the temperature? gas gets hotter more pressure more kinetic energy more collisions at greater speed
} Particles are in constant rapid random motion } They collide with the sides of the container } This exerts a force on the walls of the container } The sum of all collision forces causes Pressure This is an important concept in examinations www.cgrahamphysics.com
} Why does a balloon expand in heat? www.cgrahamphysics.com
} What happens in evaporation? High energy particles escape Average KE of particles left is now lower Energy = temperature Temperature is lower à Cooling effect www.cgrahamphysics.com
} between evaporation and boiling? Evaporation can happen well below the boiling point It only happens at the surface of the liquid Boiling happens throughout the liquid It only happens at the boiling point How can I lower the boiling point? www.cgrahamphysics.com
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} Add salt and the water will boil at a higher temperature why? Part of the pressure the solution exerts on the atmosphere now comes from solute particles, not just water molecules. The water molecules need more energy to produce enough pressure to escape the boundary of the liquid. www.cgrahamphysics.com
Temperature and absolute zero 21 of 30 Boardworks Ltd 2012
Plenary 22 of 30 Boardworks Ltd 2012 1. Draw the 3 states of matter and name the state changes. 2. Describe the motion of the particles in each state. Atomscope.exe
States of matter 23 of 30 Boardworks Ltd 2012
Converting between scales 24 of 30 Boardworks Ltd 2012