Beginner Topic 334 of 1102 Thermodynamics & Energetics
Heat
Energy transferred due to a temperature difference.
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In-depth explanation of Heat
Heat, symbolized q, is energy transferred between a system and its surroundings because of a temperature difference. Energy flows spontaneously from the hotter body to the cooler one until both reach thermal equilibrium, and no net heat flows once their temperatures are equal. Heat is a process quantity rather than a substance, so an object does not contain a fixed amount of heat in the way it contains mass. By the sign convention used in chemistry, q is positive when the system absorbs heat from its surroundings and negative when it releases heat. Measuring heat, usually through temperature changes in a calorimeter, is the basis of most experimental thermochemistry.
Going deeper: Heat
Key ideas: Heat is a transfer, not a stored quantity, and it flows only because of a temperature difference. At the molecular level it is energy passed by random collisions and radiation. Use q equals m c delta T for temperature change and q equals n delta H for phase change or reaction at constant pressure, and keep the sign convention in view.
Common mistakes and connections: Saying that an object contains heat is wrong, because it contains internal energy. Temperature and heat are also distinct: a bathtub of warm water holds more thermal energy than a cup of boiling water. This links to specific heat capacity, calorimetry and the second law, which explains why heat flows only downhill in temperature.
Visualization of Heat
Heat flows from hot to cold because fast particles pass kinetic energy to slow ones by collisions. Raise the temperature to see particle motion intensify. The interactive lesson shows this as a live animation or chart.
Worked example and use case
A hot frying pan transfers heat into the water placed on it, raising the water's temperature until the two are in balance.
Frequently asked questions about Heat
What is Heat?
Energy transferred due to a temperature difference.
Is Heat a beginner, intermediate or advanced topic?
Heat is a beginner topic in Thermodynamics & Energetics. It needs no earlier chemistry lessons and is a good starting point.
What should I learn before Heat?
Study these earlier topics in Thermodynamics & Energetics first: State Function, Path Function, Energy.
What comes after Heat?
The next topics in Thermodynamics & Energetics are Work in Chemistry and Internal Energy.
Can I practise Heat with quizzes?
Yes. The interactive lesson includes a self-check question on Heat, and the Thermodynamics & Energetics quiz draws on every topic in this area.
Where Heat fits in Thermodynamics & Energetics
Heat is topic 6 of 91 in Thermodynamics & Energetics.