When you burn a candle, or leave a cut apple in the air, a chemical change takes place. In this course we learn how to tell that a reaction has taken place, how to write it as an equation, and how to balance the equation.
3 lessons, about 1 h 15 min3 simulations10 problems6 practice questionsPython in every lesson
In a chemical reaction, the reactants change into new substances, the products. We can often tell that a reaction has taken place from a change of state, a change of colour, a gas given out, a change of temperature, or a solid that forms.
A chemical equation shows a reaction with formulae. A word equation uses the names of the reactants and products, and a skeletal equation uses the formulae but is not yet balanced. The reactants are on the left, the products on the right, and the arrow means gives. State symbols show the state, (s), (l), (g) and (aq), and conditions such as heat, light or a catalyst are written over the arrow. Never change a formula to balance an equation, and for brackets, the number outside multiplies all the atoms inside.
An equation must be balanced, with the same number of atoms of each element on both sides, because atoms are not made or destroyed. We balance by putting whole-number coefficients in front of the formulae, never by changing a formula.
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