6.4 - Thermal Energy Transfer

Question 1

What are the 2 forms of energy?

Answer 1

Kinetic and potential energy.

Question 2

What is kinetic energy created from?

Answer 2

The speed of particles.

Question 3

What is potential energy created from?

Answer 3

The separation between particles.

Question 4

What is internal energy defined as?

Answer 4

The sum of the randomly distributed kinetic and potential energies of the particles in a body. (unit is Joules)

Question 5

What 4 things is the internal energy of a system determined by?

Answer 5

• Temperature
• Random motion of molecules
• Phase of matter
• Intermolecular forces

Question 5

How can one increase the internal energy of a system?

Answer 5

• Doing work on it
• Adding heat to it

Question 6

What phase of matter has the highest and lowest internal energy?

Answer 6

• Gases have the highest
• Solids have the lowest

Question 7

What is the first law of thermodynamics?

Answer 7

The internal energy of a system is increased when energy is transferred to it by heating or when work is done on it.

Question 8

What happens to the internal energy of a gas when it’s compressed?

Answer 8

The internal energy increases due to there being less space for the gas to move around: more kinetic energy as they move faster.
- work done ON gas

Question 9

What happens to the internal energy of a gas as it expands into a greater area?

Answer 9

The internal energy decreases as there is more space for the gas to move around: less kinetic energy as they move slower.
- work done BY gas

Question 10

What is the specific heat capacity of a substance?

Answer 10

The amount of thermal energy required to raise the temperature of 1kg of a substance by 1K without a change of state.

Question 11

What are the units of specific heat capacity?

Answer 11

Joules per kilogram per Kelvin/Celsius
Jkg⁻¹K/°C⁻¹

Question 12

How does the weight of a material effect specific heat capacity?

Answer 12

The heavier the material, the more thermal energy required to raise its temperature, therefore it has a higher specific heat capacity.

Question 13

How does the amount of temperature change effect specific heat capacity?

Answer 13

The larger the change in temperature, the higher the thermal energy required to achieve this change, therefore it has a higher specific heat capacity.

Question 14

What is the equation for calculating specific heat capacity?

Answer 14

ΔQ = mcΔθ
ΔQ = change in thermal energy (J)
m = mass (kg)
c = specific heat capacity of the substance (Jkg⁻¹K/°C⁻¹)
Δθ = change in temperature (K/°C)

Question 15

What is a continuous-flow calorimeter and what does it do?

Answer 15

An apparatus that finds the specific heat capacity of a fluid.

Question 16

How do continuous-flow calorimeters calculate the specific heat capacity of a fluid?

Answer 16

• Fluid flows through an electrical heating wire
• The rise in temp of the fluid is measured using the electric thermometers
• Δθ = T2 – T1
• the mass of the fluid is found using the flow rate - mass in mass out
• Thermal losses are assumed to be equal for both flow rates

Question 17

What is the equation to find specific heat capacity from a continuous-flow calorimeter?

Answer 17

c= Q₂ -Q₁ / (m₂ - m₁)Δθ

Question 18

What is latent heat?

Answer 18

The thermal energy required to change the state of 1kg of mass of a substance without any change of temperature.

Question 19

What are the 2 types of latent heat?

Answer 19

• Specific latent heat of fusion - melting, freezing
• Specific latent heat of vaporisation - boiling, condensing

Question 20

What is the equation for specific latent heat?

Answer 20

Q= ml
Q = amount of thermal energy to change the state (J)
m = mass of substance changing state (kg)
l = latent heat of fusion/vaporisation (Jkg⁻¹)

Question 21

If a mass is greater, how is its latent heat capacity effected?

Answer 21

The greater the mass, the more energy required to change its state