Calorimetry
q = mc(deltaT)
The calorimetry equation calculates heat absorbed or released using mass, specific heat capacity, and temperature change. It's fundamental for determining enthalpy changes experimentally.
Variables
Heat absorbed (+) or released (-) in joules
Mass of substance in grams
Heat capacity in J/(g·°C)
Final temperature minus initial temperature
Example Calculation
Scenario
A 50.0 g sample of water is heated from 25.0°C to 75.0°C. Calculate the heat absorbed. (c_water = 4.18 J/g·°C)
Given Data
Calculation
q = mc(deltaT) = (50.0 g)(4.18 J/g·°C)(50.0°C)
Result
q = 10,450 J = 10.5 kJ
Interpretation
The water absorbed 10.5 kJ of heat energy. Water has a high specific heat, which is why it's commonly used in calorimetry and temperature regulation.
When to Use This Formula
- ✓Calculating heat absorbed or released
- ✓Determining enthalpy changes in reactions
- ✓Coffee cup calorimetry experiments
- ✓Finding specific heat capacity of unknown substance
Common Mistakes
- ✗Forgetting the sign of q (exo vs endo)
- ✗Using wrong specific heat value
- ✗Confusing mass of water with mass of reactant
- ✗Not converting units (J to kJ)
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Common questions about this formula
For reactions in solution: q_solution = -q_reaction (heat gained by solution = heat lost by reaction). Calculate q for solution using m (mass of solution), c (usually water's value), and deltaT. Then deltaH = q_reaction / moles of limiting reagent.
Specific heat capacity (c) is the amount of heat needed to raise 1 gram of a substance by 1°C. Water has c = 4.18 J/(g·°C), which is unusually high. Metals typically have lower values (around 0.4-0.9 J/(g·°C)).