Signs that a chemical reaction is happening include fizzing (a gas is made), a colour change, a temperature change, light or a flame, a new smell, and a precipitate: a solid forming when two solutions are mixed. Reactions that give out heat are exothermic; those that take in heat are endothermic.
A word equation shows a reaction: reactants → products. For example, magnesium + oxygen → magnesium oxide. Metals reacting with acids give a salt and hydrogen: zinc + hydrochloric acid → zinc chloride + hydrogen. Hydrogen is tested with a lit splint: it burns with a squeaky pop. Carbon dioxide turns limewater milky. Oxygen relights a glowing splint.
Worked example
Write a word equation for burning carbon in oxygen.
- Reactants: carbon and oxygen.
- Carbon joins with oxygen to make carbon dioxide.
Answer:carbon + oxygen → carbon dioxide.
Key words
- precipitate
- a solid formed when two solutions react
- exothermic
- gives out heat
- endothermic
- takes in heat
- word equation
- reactants → products, in words
New questions every time.
NGSS-referenced: MS-PS1-2