Chemical Equilibrium
At equilibrium forward and reverse rates are equal.
About this topic
Chemical equilibrium is reached in a reversible reaction when the forward and reverse rates are equal, so the concentrations of reactants and products stay constant. It is dynamic: reactions continue in both directions, but there is no net change. It occurs in a closed system and is shown with a double arrow, such as N2 + 3H2 ⇌ 2NH3.
At the start, the forward reaction is fast and the reverse is slow; as products build up the reverse speeds up while the forward slows, until the rates match. Equilibrium does not mean equal concentrations, only constant ones. Whether mostly products or reactants are present depends on the reaction and conditions. A graph of concentration against time levels off to flat lines. The same equilibrium can be reached from either direction.
Example: a sealed bottle of fizzy drink has carbon dioxide dissolved in the liquid in equilibrium with the gas above it: CO2(g) ⇌ CO2(aq). When you open it, the pressure drops, the equilibrium shifts and bubbles form. Another is the brown gas NO2 and colourless N2O4 mix in a sealed tube, where the colour stays constant once equilibrium is reached, even though molecules continue to interconvert.
Misconceptions: equilibrium means the reaction has stopped, or that concentrations are equal. Neither is true. Remember also that a catalyst does not alter the position, only the time to reach it.
Key ideas
- Concentrations stay constant
- Dynamic, not static
- Closed systems only
Quick check
Use cases: where Chemical Equilibrium helps
- Homework: review the key idea behind Chemical Equilibrium before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Chemical Equilibrium without notes.
- Visual learning: play with the interactive lab to see how Chemical Equilibrium changes when you adjust its inputs.
- Teaching a friend: explain Chemical Equilibrium in your own words, then compare your version with the key ideas.
Chemistry explains medicine, food, cleaning products, fuels and building materials.
Frequently asked questions
What is Chemical Equilibrium?
At equilibrium forward and reverse rates are equal.
What will I learn in Chemical Equilibrium?
Concentrations stay constant. Dynamic, not static. Closed systems only.
Is Chemical Equilibrium part of Chemistry?
Yes. It is one of 150 Chemistry topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the Chemical Equilibrium lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study Chemical Equilibrium?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
Do I need an account, and is my progress saved?
No account is needed. Marking a topic as learned is saved in your own browser, so it stays on that device and is not sent to a server.