Thermodynamics Problems

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Questions and Answers

What is meant by thermal equilibrium?

Thermal equilibrium occurs when two or more systems are at the same temperature, and there is no net heat transfer between them.

What is the specific heat capacity of water in J/kg°C?

4180 J/kg°C

What is the equation to calculate the temperature reached by the copper in the flame?

(m_copper x c_copper + m_water x c_water) - m_copper x c_copper x T_copper / m_water x c_water

What is the latent heat of vaporisation of steam in J/kg?

2.25 x 10^6 J/kg Signup and view all the answers

What additional data is needed to calculate the energy used to produce steam when the lump of copper enters the water?

The mass of water turned to steam Signup and view all the answers

What is the quantity of latent heat required to change the phase of 0.8 kg of R–134a if the latent heat of vaporisation is 2.17 x 10^5 J/kg?

1736000 J Signup and view all the answers

Why is the temperature of the R–134a constant when latent heat is transferred?

The temperature remains constant because the energy transferred is used to change the state of the substance, not its temperature. Signup and view all the answers

How does the arrangement of R–134a molecules change when it transitions from liquid to gas?

The molecules spread out and move further apart, gaining kinetic energy and increasing in volume. Signup and view all the answers

What is the coefficient of volume expansion of R–134a?

3.24 x 10^(-3) ºC^(-1) Signup and view all the answers

How does the emission of thermal radiation from blood vessels help to lower blood temperature?

Thermal radiation carries energy away from the blood, reducing its temperature. Signup and view all the answers

How does evaporation from the nose of a giraffe cool the blood beneath the skin?

As water evaporates, it absorbs energy from the blood, cooling it down. Signup and view all the answers

What is the function of expansion joints on a bridge?

To allow for the expansion and contraction of the bridge material due to temperature changes. Signup and view all the answers

Why is it necessary to consider the coefficient of linear expansion of steel when constructing a bridge?

To ensure that the bridge can accommodate the expansion and contraction of the material due to temperature changes. Signup and view all the answers

What is the term used to describe the process of heat transfer illustrated in the diagram?

Convection Signup and view all the answers

What is the process of heat transfer shown in the diagram?

Heat is transferred from the sun to the air, which warms the surrounding air, causing it to expand and rise, creating a circulation of air. Signup and view all the answers

Which material has the greatest increase in temperature when 3.6 x 10^6 J of heat is transferred?

Grass Signup and view all the answers

What is the final temperature of 1 m^2 of concrete after 2 hours, given an initial temperature of 5°C?

Calculation required: final temperature = initial temperature + (heat transferred / (mass x specific heat capacity)) Signup and view all the answers

What happens to the thermal energy of R-134a when it is pressurized inside the compressor?

The thermal energy of R-134a increases. Signup and view all the answers

Describe the process of heat transfer by conduction in the condenser coils.

Heat is transferred from the pressurized R-134a to the outside air through direct contact between the coils and the surrounding air. Signup and view all the answers

What is the term used to describe the transition from gas to liquid?

Condensation Signup and view all the answers

Define the latent heat of vaporization.

The amount of heat energy required to change 1 kg of a substance from a liquid to a gas at constant temperature and pressure. Signup and view all the answers

Study Notes

Temperature Conversion

45°C is equivalent to a certain temperature in °F (to be calculated)

Heat Transfer and Thermal Equilibrium

A lump of copper is heated in a Bunsen burner flame and then transferred to a beaker of water
The temperature of the water increases from 15°C to 35°C, indicating heat transfer from the copper to the water
Thermal equilibrium: when two systems (e.g. copper and flame) are in thermal equilibrium, they have the same temperature and no heat is transferred between them

Latent Heat and Phase Changes

Latent heat of vaporisation of steam is 2.25 x 10^6 J/kg
To calculate the energy used to produce steam, the mass of water turned to steam is needed
Latent heat of vaporisation of R-134a is 2.17 x 10^5 J/kg
Temperature remains constant during phase change due to absorption or release of latent heat

R-134a Properties

Boiling point of R-134a is 246.85 K (-26.15°C)
When R-134a transitions from liquid to gas, molecules gain kinetic energy and move faster and further apart
Coefficient of volume expansion of R-134a is 3.24 x 10^-3 °C^-1

Giraffe Adaptations

Giraffes have networks of blood vessels that bring warm blood to the skin, which loses heat through thermal radiation
Evaporation of water from the nose cools blood beneath the skin, which travels to the carotid rete to cool the brain

Expansion Joints

Expansion joints on bridges allow for thermal expansion and contraction of the structure
Calculation of minimum distance between two halves of a bridge to prevent damage during temperature increase

Solar Heating and Heat Transfer

Heat transfer process illustrated: convection
Process of heat transfer: solar radiation heats the ground, warming the air closest to the ground, which rises, creating an area of low pressure

Refrigerator Components

Compressor increases the temperature of R-134a through compression
Heat transfer by conduction: transfer of heat energy through direct contact between particles
Condenser: heat is transferred from pressurised R-134a to the outside air
Latent heat of vaporisation: energy required to change the phase of a substance from liquid to gas

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Description

Solve thermodynamics problems involving temperature conversion and heat transfer. Calculate temperature rise and specific heat capacity.