Changes of State

what’s the arrangement of particles in a solid

• regular

• close together

• strong forces between particles

remember- what is the thermal energy store of a substance related to

the kinetic energy store of the particles

define absolute temperature

measure of the average kinetic energy of the particles

method- temperature time graph

1. fill beaker with crushed ice and place a thermometer in beaker

2. allow thermometer to equilibrate and record the temp

3. using a bunsen burner gradually heat beaker

4. every 20 seconds record the state and temperature to the ice

5. stir to allow even distribution of temperature

6. continue until water boils

7. plot a graph of temperature against time

8. read the thermometer at eye level to avoid parallax error

9. use a temperature sensor and data logger to take more readings at smaller intervals

why is temperature constant at the melting point

• heat energy being supplied is used to overcome the intermolecular bond between molecules rather than being use to raise the temperature

• the average KE of the particles doesnt change

why is temperature constant at the boiling point

• all energy is used to overcome forces of attraction between the molecules

• average KE of particles doesnt change

why is temperature constant at the condensing or freezing point

• bonds between particles are forming

• so energy is released

• keeping temperature constant

explain the difference evaporation and boiling

evaporation

• occurs at any temperature

• particles leave liquid from its surface

• slower

• leads to cooling

• produces no bubbles

boiling

• only occurs at the boiling point

• occurs throughout the liquid

• faster

• produces lots of bubbles

how does evaporation lead to cooling

• temperature is a measure of average kinetic energy of the particles

• particles with most KE and are travelling in the right direction have sufficient energy to overcome the attractive forces and escape the liquid from its surface

• meaning the average KE of the remaining particles falls

• so the temperature falls

explain the changes that occur when a solid melts

• particles gain KE

• bonds weaken between particles

• particles go from a regular arrangement to irregular

• particles go from vibrating about a fixed position to slipping and sliding past each other

define specific heat capacity

the energy needed to raise the temperature of 1Kg of the substance by 1degreeC

what does S.H.C tell us

a substance with a high s.h.c needs lots of energy to raise their temperature by 1degree C

heating curve for ice, water, steam:

1. what does a steeper gradient tell us about s.h.c

2. why is the gradient of each section different

1. steeper the gradient the lower the s.h.c

2. each state of water has different s.h.c and therefore increase in temp at different times

method- measure the s.h.c of an object

1. measure the mass of the block using a balance

2. turn on the heater and start the stop watch at the same time

3. record initial temp of block time=0s

4. record current from ammeter, voltage from voltmeter

5. record the temp every minute for 10 mins

6. calculate energy at each time E=P x t = IV x t

7. plot temp against energy

8. gradient = 1 over m x c

9. s.h.c = 1/gradient x m

why might value for s.h.c be too high

• some thermal energy is lost to the surroundings

• therefore not all energy is heating the block

• and change in temperature is too small

• (so gradient of line isn’t steep enough)

why do we place a small amount of water in the hole where the thermometer goes during the experiment

1. so there is a good thermal contact between the block and the thermometer