THERMAL ENERGY
Thermal energy is the same as heat or heat or heat energy
Temperature is not the same thing as heat
We use different units of measurement for these two things:
 Temperature is measured in _______
 Heat is measured in ________

TEMPERATURE AND HEAT
Temperature is a measure of the AVERAGE amount of energy in a substance, and is measured in °C ⁰F. and K
Conversions: ° C = K – 273 : K = C + 273
If the temperature increases by 10 °C, how much does it increase in K?
Heat is related to temperature but the two are not the same.
Which has a higher temperature? A space heater or a candle?
Which one can make a room warmer?

DIFFERENCE BETWEEN HEAT AND TEMPERATURE
You add the same amount of heat energy (for example 50,000J) to both you would find that the temperature of the cup of water increases by much more than the temperature of the bucket of water.

HEAT TRANSFER
Heat can be transferred in three ways.
1.
Conduction - by a substance which does not move (solids).
2.
Convection - by substance which moves (liquids and gasses).
3.
Radiation - infra-red radiation is exchanged between all substances.
Heat is transferred naturally from a substance with a higher temperature to a substance with a lower temperature.
If two objects have the same temperature, they will not transfer energy and are said to be tin thermodynamic equilibrium

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THERMAL ENERGY
The energy required to raise a kg of an object by 1 degree is different for different substances.
For example:
 To heat 1kg of copper from 20°C to 21°C requires 390J,
 To heat 1kg of aluminium from 20 to 21°C takes 910J.
 This is known as the SPECIFIC HEAT CAPACITY of a substance.
 Specific heat units:
𝐽
𝐾𝑘𝑔

SPECIFIC HEAT CAPACITY
The specific heat capacity of a substance is the amount of heat energy required to raise the temperature of the substance unit mass by a unit change in temperature.
The unit mass is usually 1kg, while the unit change in temperature is 1K or 1°C. The key formula is:
Energy = specific heat capacity × mass × change in temperature

SPECIFIC HEAT CAPACITY
Calculate the following:
 How much energy is needed to increase the temperature of 500 g of lead from 20
ºC to 45 ºC? The specific heat capacity of lead is 128 J/kg/ºC.

HEAT TRANSFER
Complete the following definition using the words below:
___________ energy or heat is always transferred from a _________ place to a
___________ place. The amount of energy _____________ depends on how big the _______________ difference is cooler thermal transferred hotter temperature

SPECIFIC HEAT CAPACITY
• Specific Heat : C
• Change in Temperature: ∆T , 𝑻 𝒇
− 𝑻 𝒊
• Mass : m
• Energy, Heat: Q
Rearrange this equation to solve for m, C, Tf, Ti

REVIEW
Use the table on page 318 of the textbook to assist you in answering this question:
How much heat is required to raise the temperature of a 2.3kg copper pipe from 20 ⁰C to 80⁰C?
𝑄 = 𝑚𝐶∆𝑇
𝐽
𝑄 = 2.3𝑘𝑔 × 385 𝑘𝑔𝐾
Q = 53,130J
× 60℃

REVIEW
Use the table on page 318 of the textbook to assist you in answering this question:
50,000J of heat are added to a 10kg bucket of water. How much would you expect the temperature to increase?
𝑄 = 𝑚𝐶∆𝑇
50,000J = 10kg × 4810
𝐽 𝑘𝑔𝐾
× ∆𝑇
∆𝑇 =
50,000𝐽
4810𝐽/𝑘𝑔𝐾∗10𝑘𝑔
= 1.2K

REVIEW
Use the table on page 318 of the textbook to assist you in answering this question:
The temperature of a block of Aluminum increases from 250K to 300K as it absorbs
4000J of heat. What is the mass of the block?
𝑄 = 𝑚𝐶∆𝑇 m = Q/(C∆T) = 4000J/(897J/kgK*50K) = .089kg
= 89g

CONSERVATION OF THERMAL ENERGY
• As with any isolated system, the total amount of energy in a closed system is constant.
• If a system involved contact between two different objects, the total energy of the two blocks would remain constant:
• 𝑬 𝒂
+ 𝑬 𝒃
= 𝒄𝒐𝒏𝒔𝒕𝒂𝒏𝒕
• For this to be true when energy is exchanged,
• ∆𝑬 𝒂
= −∆𝑬 𝒃
• Total energy in the system does not change

WHEN HEAT IS THE ONLY FORM OF ENERYGY
EXCHANGED
∆𝑬 = 𝑸 = 𝒎𝑪∆𝑻 𝒎 𝒂
𝑪 𝒂
∆𝑻 𝒂
+ 𝒎 𝒃
𝑪 𝒃
∆𝑻 𝒃
= 𝟎
• What must be the relationship between the temperature changes of A and B?
• Objects will exchange energy until they reach the same final temperature
• 𝑻 𝒇
= 𝒎
𝑨
𝑪
𝑨 𝒎
𝑨
𝑻
𝑨
+𝒎
𝑩
𝑪
𝑩
𝑻
𝑩
𝑪
𝑨
+𝒎
𝑩
𝑪
𝑩

CALCULATIONS OF EQUILIBRIUM TEMPERATURE
A 200g sample of water at 80C is mixed with 300g of water at 10C. What is the final temperature of the mixture?
𝑻 𝒇
= 𝒎
𝑨
𝑪
𝑨
𝑻
𝑨
+𝒎
𝑩
𝑪
𝑩
𝑻
𝑩 𝒎
𝑨
𝑪
𝑨
+𝒎
𝑩
𝑪
𝑩
𝑻 𝒇
=
.2𝑘𝑔∗353𝐾+ .3𝑘𝑔∗283𝐾
.5𝑘𝑔
=311K

A .5kg lead weight at a temperature of 100 ⁰C is dropped into 1kg of water at 35⁰C. What is the final temperature of the water and weights?
𝑻 𝒇
= 𝒎
𝑨
𝑪
𝑨
𝑻
𝑨
+𝒎
𝑩
𝑪
𝑩
𝑻
𝑩 𝒎
𝑨
𝑪
𝑨
+𝒎
𝑩
𝑪
𝑩
𝑇 𝑓
Tf = 36 ⁰C
=
.5𝑘𝑔 ∗
130𝐽 𝑘𝑔𝐾
∗ 100𝐶 + 1𝑘𝑔 ∗
4180𝐽 𝑘𝑔𝐾
.5𝑘𝑔 ∗
130𝐽 𝑘𝑔𝐾
+ 1𝑘𝑔 ∗
4810𝐽 𝑘𝑔𝐾
∗ 35𝐶

PHASE CHANGE
• What is the temperature of ice water ?
• What is the temperature of Boiling water?
• How does the device in the picture work?
• Why do we sweat?

STATES OF MATTER
• Solid (fixed volume, shape)
• Liquid(fixed volume, variable shape)
• Gas (variable volume, variable shape)
• At various temperatures, and pressures, substances can change between these three states of matter.

STATES OF MATTER
• Melting point- Substance changes from solid to liquid
• Boiling point – Substance changes from liquid to gas
• Sublimination- Substance changes directly from solid to gas.

ENERGY
• The more energy a molecule has, the more kinetic energy it has.
• The more kinetic energy, the more a molecule is free to move. Resulting in changes in its state.
• When heat is added to a system, some of the energy is converted into kinetic energy of the molecules instead of thermal energy.

BOILING A KG OF WATER

ENERGY OF PHASE CHANGE
• During a phase change Temperature does not increase even though thermal energy exchanged
• Melting- 273K ice becomes 273K water
• Heat is Absorbed
• Freezing – Heat is Released
• Boiling - Heat is absorbed
• Condensing – Heat is released

HEAT OF VAPORIZATION
The energy required to convert Ikg of a substance between liquid and gaseous states
Gas to liquid 𝑯 𝒗
𝑸 = 𝒎𝑯 𝒗
Liquid to Gas 𝑯 𝒗 𝒊𝒔 𝒑𝒐𝒔𝒊𝒕𝒊𝒗𝒆 is negative

IMPLICATIONS OF PHASE CHANGE
• When a liquid evaporates, it absorbs heat from its environment. ( Cooling )
• When liquid condenses, it releases heat to the environment (Warming)

HEAT OF FUSION
• The energy required to change a1kg of a substance between solid and liquid states
•
𝑓
•
•

PRACTICE
How much heat is absorbed by a 50 g ice cube as it melts to become liquid water at 273K?
𝑄 = 𝑚𝐻 𝑓
Q = .05kg*3.34* 10
5 𝐽 𝑘𝑔
Q = 16,700J

PRACTICE
Do you expect a soda can to get warmer or colder as water condenses on the outside?
• Warmer

KINETIC ENERGY AND HEAT
A .005kg bullet is travelling at 200m/s. What is its kinetic energy?
𝐾𝐸 =
1
2 𝑚𝑣 2 = 1𝑘𝐽
If the bullet is stopped by a block of ice, how much water is formed?
𝐴𝑠𝑠𝑢𝑚𝑒 𝐾𝐸 𝑏𝑒𝑐𝑜𝑚𝑒𝑠 𝑡ℎ𝑒𝑟𝑚𝑎𝑙 𝑒𝑛𝑒𝑟𝑔𝑦
Q = m* 𝐻 𝑓
1,000J = m*334,000J/kg m = .003kg = 3g of water

MULTIPLE STEPS
How much energy is required to completely boil
2kg of water initially at a temperature of
50 ⁰C?
Step 1: Heat water to 100⁰C :
Step 2 Evaporate water to steam at
100 ⁰C :
Q = mC∆T
Q = 𝒎𝑯 𝒗
𝑄 = 𝑚𝐶∆𝑇 + 𝑚𝐻 𝑣
Q = 2kg*2180J/kgK*50K + 2kg*2.26* 10 6 = 4.5 ∗ 10 6 𝐽