Notes On Heat Calculations

1. Write down unknown information (i.e. what you are looking for).

2. Write down what you know. Remember if you are given heat value (in cal or J) you need to determine the sign of this value:

• What to do with heat term
  • If system is losing heat (giving to surrounding), the heat sign is negative
  • If system is gaining heat (absorbing from surrounding), the heat sign is positive
  • If you are calculating the heat value, you don't determine the sign your calculations will

• What to do with temperature and temperature change
  • Show You must show T_initial and T_final
  • ,Show calculation, ΔT = T_final - T_initial HERE including sign
  • If your unknown is either T_initial or T_final, see special case below

3a. Setting up answer: By equation (Following steps from Set-up for Equations Notes)

• Equation for Phase change (called Latent heat) heat equation (equ): In class
• Equation for Non-phase change (calledSensible heat) heat equ: ΔH = ( m ) ( ΔT ) ( c )
  • where ΔH is heat change, ΔT is temperature change and c is specific heat capacity (J/(g-°C) or cal/(g-°C))

3b. Setting up answer: By Dimensional Analysis (Following steps from Dimensional Analysis Notes

• Important information is that c (specific heat capacity) is conversion: unit for c = J/(g-°C) or cal/(g-°C)
  

4. Do math. (make sure to have units on all numbers and keep appropriate sig fig and scientific notation).

5. Check answer including correct number of sig figs, scientific notation, and proper units! Remember that the last calculation step determines the method of determining sig figs.

Example of Work

• [Example of Work for Most Basic Heat Calculations]
• [Example of Work for Basic Heat Calculations]
• More Complicated or Advanced Problems (Usually Honors Learner)
  
  • [Example of Work for Heat Calculation where Sign of Heat Matters]

For these problems, the actual equation/math you are trying to solve is not the heat equation ΔH = (m)(ΔT)(c) but ΔT = T_final - T_initial
So, you will need to change the above equation to either:

• T_final = ΔT + T_initial or
• T_initial = ΔT - T_final

• Note: since last math step is add/subtract, you will need to do columns/decimal places not number of sig fig to get answer in correct sig figs.
  

• [[Example of Work for Heat Calculation for Initial or Final Temperature]]