Beginner Topic 333 of 1102 Thermodynamics & Energetics
Energy
The capacity to do work or transfer heat, measured in joules.
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In-depth explanation of Energy
Energy is the capacity to do work or to transfer heat, and it exists in several forms: kinetic, potential, thermal, chemical, electrical and radiant. The first law of thermodynamics states that energy is conserved, so it is never created or destroyed but only converted from one form to another. The SI unit is the joule, defined as one newton metre, and the calorie is an older unit equal to exactly 4.184 joules. In chemistry, energy is stored in the arrangement of electrons within bonds and in the relative positions of molecules, and it is released or absorbed when bonds are rearranged in a reaction. Recognizing these conversions is central to understanding fuels, batteries and biological metabolism.
Going deeper: Energy
Key ideas: Learn to convert freely between joules, kilojoules, calories and electron volts. Chemical energy changes are usually per mole, so a value in kJ per mol must be multiplied by the moles actually reacting. Kinetic energy depends on motion and potential energy on position or arrangement, and chemical potential energy is stored in bonding arrangements.
Common mistakes and connections: Energy is not a substance that is used up, since it is only transformed, and some of it ends up as dispersed thermal energy that is hard to recover. Do not confuse energy with power, which is energy per unit time in watts. This topic is the foundation for the first law and for energy density comparisons of fuels.
Visualization of Energy
Energy appears as kinetic, potential, thermal and chemical forms and converts among them, but the total is conserved. Illustrative equal slices of the forms discussed. The interactive lesson shows this as a live animation or chart.
Worked example and use case
Burning gasoline in an engine converts stored chemical energy into thermal energy and then into mechanical motion.
Frequently asked questions about Energy
What is Energy?
The capacity to do work or transfer heat, measured in joules.
Is Energy a beginner, intermediate or advanced topic?
Energy is a beginner topic in Thermodynamics & Energetics. It needs no earlier chemistry lessons and is a good starting point.
What should I learn before Energy?
Study these earlier topics in Thermodynamics & Energetics first: Open Closed Isolated Systems, State Function, Path Function.
What comes after Energy?
The next topics in Thermodynamics & Energetics are Heat and Work in Chemistry.
Can I practise Energy with quizzes?
Yes. The interactive lesson includes a self-check question on Energy, and the Thermodynamics & Energetics quiz draws on every topic in this area.
Where Energy fits in Thermodynamics & Energetics
Energy is topic 5 of 91 in Thermodynamics & Energetics.