Chemical Equation
Definition and meaning of Chemical Equation in chemistry.
A chemical equation is a symbolic representation of a chemical reaction, showing the formulas of reactants and products separated by an arrow indicating the direction of reaction.
In more detail
A properly written chemical equation must be balanced, meaning the same number of atoms of each element appears on both sides, in accordance with the law of conservation of mass. Coefficients placed before formulas adjust the relative amounts of each substance without changing the subscripts within a formula, since altering subscripts would change the substance's identity. Equations may also include state symbols (s, l, g, aq) and, for reactions that release or absorb heat, an enthalpy term to convey additional information about the process.
Key facts
| Field | General Chemistry |
|---|---|
| Key principle | Law of conservation of mass |
| Balancing method | Adjust coefficients, never subscripts |
| Common symbols | → (yields), (s), (l), (g), (aq) |
The balanced equation for methane combustion is CH4(g) + 2O2(g) → CO2(g) + 2H2O(l), showing one carbon, four hydrogen, and four oxygen atoms on each side.
Frequently asked questions
Why must a chemical equation be balanced?
Because atoms are neither created nor destroyed in a chemical reaction, the total number of atoms of each element must be equal on the reactant and product sides.
What is the difference between a coefficient and a subscript in an equation?
A coefficient is a number placed in front of a formula to show how many molecules or formula units react, while a subscript is part of the formula itself and shows how many atoms are bonded within one unit; changing a subscript creates a different substance.