Notesale: Turn your study into money

Document Preview

Extracts from the notes are below, to see the PDF you'll receive please use the links above

---

Thermal Properties of Matter

(a) Internal energy (Distinguish between internal energy, temperature and thermal energy)
•

The internal energy of a body is the sum of the total random kinetic energies and total
intermolecular potential energies of all the molecules inside it
...
This is
measured as an increased temperature
...


(b) Heat capacity
Heat capacity C is the amount of thermal energy required to raise the temperature of a substance by 1 K (or
1°C)
...

𝐶
𝑄
𝑐= =
𝑚 𝑚∆𝜃
A substance with a high c heats up more slowly compared to a substance with a lower c (and vice versa)
This is important in heating and cooling systems, e
...
water is used in heating and cooling systems because
it has high c
...


1

Question 1
Determine the quantity of heat required to raise the temperature of 100 g of ice from −20°C to −5°C
...

Determining specific heat capacity c of a substance (Calorimetry)

•
•
•
•
•

Supply a known amount of energy from an electric heater placed inside the substance
...
The
process involves surrounding it with a material that traps air (a poor conductor) and is known as lagging
...
Calorimeters are used in these experiments as they are designed to
limit thermal energy transfer to, or from, the surroundings
...
0 min to raise the
temperature of 450 g of aluminium from 27°C to 50°C
...
0 K, and 200 s to heat up a piece of copper by
10 K
...


Question 4
A piece of hot coal of mass 50 g at a temperature of 200°C is dropped into 150 g of water at a temperature
of 25°C
...
(The specific heat capacity of coal and water are 710 J kg K
−1 −1
and 4200 J kg K respectively
...


2

Question 5
A large metal bolt, of mass 53
...
The bolt was transferred
as quickly as possible from the oven into a beaker containing 257
...
1°C
...
5 °C
...

(b) Why was the bolt kept in the oven for a long time?
(c) Why was the transfer made quickly?
(d) Calculate the specific heat capacity of the material of which the bolt is made
...


(d) Change of state
• Thermal energy, which causes a change of state, is known as latent heat
...
The potential energy of the molecules increase
...


Boiling

Boiling is the process in which the thermal energy absorbed by a substance changes it
from liquid state to gaseous state without a change in temperature
...


Freezing

Freezing is the process in which the thermal energy taken away from a substance changes
it from liquid state to solid state without a change in temperature
...
The liquid requires latent heat of vaporization
which is from the liquid or its surroundings
...

Molecules in a liquid have a range of different kinetic energies that are continuously transferred between
them as they collide
...

The average kinetic energy of the molecules remaining decrease resulting in cooling
Evaporation occurs at the surface of the liquid and at any temperature, with the rate of evaporation
increasing with rising temperature

3

Differences between boiling and evaporation

(f) Latent Heat
• The thermal energy involved with changing potential energies during a change of state is known
as latent heat
...
The latent heat
associated with boiling or condensation is called latent heat of vaporization
...
From P to Q, the temperature of solid ice rises
from −15°C to 0°C
...
From Q to R, the temperature remains steady
at 0°C, even though heat is being absorbed as
ice melts
...
From R to S, the temperature of melted ice
rises from 0°C to 10°C
...
From A to B, the temperature of naphthalene
falls from 90°C to 79°C
...
From B to C, the temperature remains steady
at 79°C, even though heat is being released as
solidification occurs
...
From C to D, the temperature of solid
naphthalene falls from 79°C to room
temperature
...
00 kg of water at 100 C requires 4400 kJ of energy to boil off completely
...


Question 7
A 1
...
In the five
minutes, the ice melts and the temperature of the melted water rises to 49°C
...

Where does the thermal energy go?
Solution
The thermal energy absorbed is used to overcome intermolecular bonds in order for the solid to melt
...


Question 9
1 kg of ice at −10°C is heated until it becomes steam at 100°C
...
(c of ice = 2100 J/(kgK), lf = 3
...

Q1 =
• At 0°C:
Melting occurs and the thermal energy absorbed is used to overcome/weaken the bonds between the
molecules such that they have greater freedom of motion in the liquid state
...
The kinetic energy of the
molecules increases and the molecules move more quickly
...

Q4 =
6

• 100°C to 110°C:
The thermal energy absorbed is used to raise the temperature of the water vapour molecules
...

Q5 =

7

(i)

Cooling curve summary

8

June 1986
2
...
It is found that exactly 14 hours
elapse before the contents of the flask are entirely water at 0 C
...
4 ×10 J/kg calculate the average rate at which the contents gain heat from the surroundings
...


Nov 81
Liquid nitrogen boils at a very low temperature, at normal atmospheric pressure

---