Energy Changes in Systems

These revision notes cover the section on Energy Changes in Systems assessed as part of the AQA GCSE Physics and Combined Sciences: Trilogy qualifications.

thermometer diagram demonstrating changes in thermal heat energy

 

Understanding energy changes within systems is crucial for grasping how energy is stored or released when a system undergoes temperature changes. This concept is not just a cornerstone of physics but also finds applications in everyday life, from the workings of household appliances to large-scale industrial processes.

Thermal Energy and Temperature Change

Thermal energy is the collective kinetic energy of particles within a substance. It’s important to distinguish between thermal energy and temperature; while thermal energy refers to the total energy of all particles, temperature measures the average energy per particle. A change in temperature, therefore, indicates a change in the average kinetic energy of the particles in a system.

Calculating Change in Thermal Energy

The change in thermal energy when the temperature of a substance changes can be calculated using the formula:

ΔE = m * c * Δθ

Where:

  • ΔE is the change in thermal energy in joules (J),
  • m is the mass in kilograms (kg),
  • c is the specific heat capacity in joules per kilogram per degree Celsius (J/kg°C),
  • Δθ is the temperature change in degrees Celsius (°C).

This equation allows us to understand how much energy is needed to heat or cool a substance by a certain amount.

Specific Heat Capacity

The specific heat capacity of a substance is a measure of how much energy is required to raise the temperature of 1 kg of the substance by 1°C. It is a unique property of each material and plays a crucial role in determining how substances respond to energy changes.

Practical Application: Measuring Specific Heat Capacity

bunsen burner demonstrating thermal energy required to heat an object

Determining the specific heat capacity of a material involves measuring how much energy is required to change its temperature. This practical activity helps to understand the relationship between energy input and temperature change, underpinning many processes in physics and engineering.

Setup and Procedure

  1. Measure the mass of the material.
  2. Heat the material using a known energy source, recording the initial and final temperatures.
  3. Calculate the change in temperature (Δθ).
  4. Given the energy supplied, use the equation ΔE = m * c * Δθ to calculate the specific heat capacity (c).

Example Calculation

Imagine you’re heating a 2 kg block of iron (with a specific heat capacity of 450 J/kg°C) to increase its temperature by 10°C. The energy required for this process is calculated as:

ΔE = 2 kg * 450 J/kg°C * 10°C = 9000 J

This calculation shows that 9000 joules of energy are needed to achieve the desired temperature increase in the iron block.

Summary

Mastering the calculation of changes in thermal energy and understanding specific heat capacity are foundational in physics. These concepts are not only academically relevant but also have practical applications in a variety of fields, from designing heating and cooling systems to understanding natural phenomena.

Video on Specific Heat Capacity

 

Quiz on Energy Changes in Systems

Question 1: What does thermal energy represent?

  • A) The total kinetic energy of all particles in a substance
  • B) The total potential energy of all particles in a substance
  • C) The average potential energy of particles in a substance
  • D) The average kinetic energy of particles in a substance

Question 2: If the mass of a substance is 5 kg, its specific heat capacity is 420 J/kg°C, and the temperature change is 15°C, what is the change in thermal energy?

  • A) 28,000 J
  • B) 12,600 J
  • C) 63,000 J
  • D) 31,500 J

Question 3: What does the specific heat capacity of a substance indicate?

  • A) The amount of heat required to change its state from solid to liquid
  • B) The amount of energy required to raise the temperature of 1 kg of the substance by 1°C
  • C) The amount of energy required to raise the temperature of 1 g of the substance by 1°C
  • D) The amount of energy needed to melt 1 kg of the substance

Question 4: In a practical experiment to determine the specific heat capacity of copper, if the mass of the copper is 2 kg, the energy supplied is 9,000 J, and the temperature change is 10°C, what is the specific heat capacity of copper?

  • A) 450 J/kg°C
  • B) 225 J/kg°C
  • C) 900 J/kg°C
  • D) 90 J/kg°C

Question 5: Why is water often used as a coolant in various applications?

  • A) Because it has a low specific heat capacity
  • B) Because it has a high specific heat capacity
  • C) Because it is easily available
  • D) Because it can absorb a large amount of heat without a significant change in temperature

Answers

Answer 1: A) The total kinetic energy of all particles in a substance. This is because thermal energy is directly related to the movement and vibration of particles within a substance.

Answer 2: D) 31,500 J. Using the formula ΔE = m * c * Δθ, the calculation is 5 kg * 420 J/kg°C * 15°C = 31,500 J.

Answer 3: B) The amount of energy required to raise the temperature of 1 kg of the substance by 1°C. Specific heat capacity is a measure of a substance’s thermal inertia, indicating how much energy is needed to change its temperature.

Answer 4: A) 450 J/kg°C. To find the specific heat capacity (c), use the rearranged formula c = ΔE / (m * Δθ), which gives 9,000 J / (2 kg * 10°C) = 450 J/kg°C.

Answer 5: B) Because it has a high specific heat capacity. Water’s high specific heat capacity means it can absorb a lot of heat before its temperature increases significantly, making it an effective coolant.