Mendeleev · science lesson

Gibbs free energy and spontaneity

At constant temperature and pressure, ΔG helps determine the thermodynamically favorable direction of a transformation.

Start with the idea

At constant temperature and pressure, ΔG helps determine the thermodynamically favorable direction of a transformation.

A concrete example

ΔG < 0 indicates a thermodynamically favorable change under the stated conditions, not necessarily a fast reaction.

Mendeleev

Mendeleev’s tip

Do not start with a formula. Identify what changes, what stays constant and which quantity you are trying to explain or calculate.

Go one step deeper

The relation ΔG = ΔH − TΔS shows why temperature, enthalpy and entropy must be considered together.

Common trap

A trend or model is not an exceptionless law. Always check the quantity’s definition and the conditions being compared.

Check your understanding

Can you explain the phenomenon in your own words before looking at an equation?

Go deeper in Science →

Understand it before converting

Energy is not just a classroom quantity: it appears constantly in electricity, food, heating, mechanics and physics. Units are chosen for practical reasons. Some are convenient in everyday life, while others dominate scientific or technical work. This page deliberately focuses on familiar units — joules, kilojoules, watt-hours, kilowatt-hours, calories and kilocalories — instead of presenting a long catalogue of rarely used formats. Every pair links to a dedicated conversion page with the calculation rule, worked examples and useful reference values. The aim is to get the answer quickly while still understanding what is being converted and whether the result makes physical sense.

Energy