Heat vs Temperature and Energy Transfer in Reactions
Quick Notes:
- Chemical reactions involve energy transfers between the system and the surroundings.
- Total energy is conserved — energy is not lost, just transferred or transformed.
- Heat (q) is energy in transit due to a temperature difference.
- Temperature (T) is a measure of average kinetic energy of particles.
- Heat is measured in joules (J); temperature is measured in degrees Celsius (°C) or Kelvin (K).
Full Notes:
Every chemical reaction involves energy being absorbed or released. The reaction system may gain or lose energy, but the total energy of the universe remains constant (law of conservation of energy).
Energy is never created or destroyed – only transferred between system and surroundings.
System: the reacting chemicals.
Surroundings: everything else (container, air, solution).
In chemistry, we usually measure energy changes by observing the surroundings, especially via temperature changes (see Topic 1.1.4).
Heat vs Temperature
Heat and temperature are not the same:
- Heat = energy transferred
- Temperature = measure of average kinetic energy of particles in a system
| Property | Heat (q) | Temperature (T) |
|---|---|---|
| Definition | Energy transferred due to temperature difference | Measure of average kinetic energy of particles |
| Unit | Joules (J) | Celsius (°C) or Kelvin (K) |
| Depends on | Mass, specific heat capacity, temperature change | Particle motion only |
| Can be transferred? | Yes | No — it is a measure, not a form of energy |
Heat flows from hot to cold.
A substance with a higher temperature doesn't always have more heat
For ExampleA cup of boiling water has a higher temperature, but much less heat than a bathtub of warm water.
Conservation of Energy
During a chemical reaction:
- Exothermic: Energy released → surroundings get warmer.
- Endothermic: Energy absorbed → surroundings get cooler.
The amount of energy lost by one part of the system is gained by another — total energy stays the same.
What is the relationship between temperature and the kinetic energy of particles?
Temperature is directly related to the average kinetic energy of the particles in a substance. As temperature increases, the particles move faster because their kinetic energy increases.
Summary
- Heat = energy transferred due to temperature difference.
- Temperature = measure of average kinetic energy of particles.
- Total energy is conserved in chemical reactions — energy lost by one part of a system is gained elsewhere.