Calculating energy changes

• What is the first step in identifying a system undergoing a temperature change?

  Define the boundaries of the system
• Why is it important to identify the material within the system?

  To understand how it undergoes temperature change
• Why is it necessary to convert mass to kilograms?

  To ensure consistency in measurement units
• What does determining how the system's thermal energy changes involve?

  Assessing the increase or decrease in energy
• If you have 250 grams of water, how do you convert it to kilograms?

  Convert to 0.25 kg
• What should you do after identifying the substance in the system?

  Weigh the substance if possible
• What are specific heat capacity values for common substances?

  • Water: 4200 J/kg°C
  • Aluminium: 900 J/kg°C
  • Copper: 385 J/kg°C
• What are the units for specific heat capacity $c$?


  Joules per kilogram per degree Celsius (J/kg°C)
• How much energy is required to raise the temperature of 1 kg of a substance by 1 °C?

  It is equal to the specific heat capacity $c$
• What does $\Delta E$ represent in the formula?


  Change in energy
• What is the unit of mass used in the weighing step?

  Grams (g) or kilograms (kg)
• How is temperature change calculated?

  By subtracting initial temperature from final temperature
• What might happen if units are omitted when stating energy values?

  It could lead to confusion and misinterpretation
• What specific heat capacity value should you use for heating copper?

  385 J/kg°C
• How do you calculate the energy change for heating water?

  • Use the formula: $\Delta E =$$mc\Delta \theta$
  • Example:
  • Mass: 0.5 kg
  • Specific heat capacity: 4200 J/kg°C
  • Temperature change: from 20°C to 80°C
  • Calculation: $\Delta E =$$0.5 \times 4200 \times (80 - 20)$
  • Result: $\Delta E =$$126,000 \, \text{J}$
• What does specific heat capacity $c$ measure?


  Energy needed to raise temperature of 1 kg
• What does the formula $\Delta E =$$mc\Delta \theta$ represent?


  It calculates energy changes based on temperature change
• What specific heat capacity value should you use for heating aluminium?

  900 J/kg°C
• What specific heat capacity value should you use for heating water?

  4200 J/kg°C
• How do specific heat capacities of water, aluminium, and copper compare?

  Water has the highest specific heat capacity
• What is the energy change when heating 0.5 kg of water from 20°C to 80°C?

  126,000 Joules
• What does $\Delta \theta$ represent in the formula?


  Change in temperature
• If you calculated $\Delta E =$$126,000$, what should you do next?


  State the energy change with units
• What are the actions involved in determining the mass of a system?

  1. Identify the substance
  2. Weigh the substance
  3. Convert to kilograms if necessary
• What is the formula to calculate temperature change?

  $\Delta \theta =$$\theta_{f} - \theta_{i}$
• What are the steps to calculate temperature change?

  1. Identify the initial temperature ($\theta_{i}$)
  2. Identify the final temperature ($\theta_{f}$)
  3. Subtract $\theta_{i}$ from $\theta_{f}$
  4. Write the temperature change with units (°C or K)
• What unit should be included when stating energy change?

  Joules (J)
• What is the first step to determine the mass of a system?

  Identify the substance in the system
• What does $c$ represent in the formula?


  Specific heat capacity
• If the energy change calculated is $\Delta E =$$126,000$, how should it be stated with units?


  Energy change $\Delta E =$$126,000 \, \text{J}$
• What is the unit for energy?

  Joules (J)
• Why is it important to convert temperatures to Celsius or Kelvin?

  To ensure accurate calculations of temperature change
• What does $m$ represent in the formula?


  Mass
• Why is it important to clearly express the value of energy change?

  To ensure accurate communication of results
• Why is it important to state the final energy value with units?

  For clarity and precision in communication
• What is the final unit for mass after conversion?

  Kilograms (kg)
• What are the units for mass $m$?


  Kilograms (kg)
• What are the units for $\Delta \theta$?


  Degrees Celsius (°C)
• What are the units for $\Delta E$?


  Joules (J)
• What are the steps to evaluate energy change after calculation?

  1. Review the value obtained from the formula
  2. State the energy change with units