Exothermic & Endothermic Reactions and Patterns of Reactivity

Vocabulary flashcards covering energy changes in reactions, examples, reactivity series, displacement, and chemical equations.

Exothermic reaction

A chemical reaction that transfers energy to the surroundings, causing the temperature of the surroundings to increase.

Endothermic reaction

A chemical reaction that absorbs energy from the surroundings, causing the temperature of the surroundings to decrease.

Conservation of energy (in chemistry)

Principle stating that the total amount of energy in the universe remains constant before and after a chemical reaction.

Combustion reaction

A rapid exothermic oxidation of a substance that typically produces heat, light, and new products such as oxides.

Oxidation reaction

A reaction in which a substance gains oxygen or loses electrons; many are exothermic.

Neutralisation reaction

Reaction between an acid and a base producing a salt and water; usually exothermic.

Thermal decomposition

An endothermic reaction in which a single compound breaks down into two or more substances when heated.

Self-heating can

A practical application of an exothermic reaction used to warm food or drinks without external heat.

Hand warmer

A device that releases heat via an exothermic reaction, often involving iron oxidation.

Instant ice pack

A first-aid item that becomes cold through an endothermic reaction, commonly between ammonium nitrate and water.

Reactivity series

A ranked list of metals from most to least reactive, used to predict reaction outcomes.

Magnesium (Mg) in reactivity series

A highly reactive metal that can displace zinc, iron, and copper from their compounds.

Copper (Cu) in reactivity series

A relatively unreactive metal that cannot displace magnesium, zinc, or iron from their compounds.

Displacement reaction

A reaction in which a more reactive metal displaces a less reactive metal from its compound.

Acid–metal reaction

General reaction where a metal reacts with an acid to form a salt and hydrogen gas.

General word equation for acid–metal reaction

metal + acid → salt + hydrogen

Burning splint ‘pop’ test

Laboratory test where a lit splint makes a ‘pop’ sound in hydrogen, confirming the presence of hydrogen gas.

Reactants

Substances present at the start of a chemical reaction, written on the left side of a chemical equation.

Products

Substances formed during a chemical reaction, written on the right side of a chemical equation.

Word equation

A chemical equation that uses only the names of reactants and products, without chemical symbols.

Balanced symbol equation

A chemical equation that shows correct formulas and equal numbers of each type of atom on both sides.

Coefficient (in equations)

A number placed in front of a chemical formula to balance the number of atoms in an equation.

Magnesium + hydrochloric acid reaction

Mg + 2HCl → MgCl₂ + H₂; a fast reaction producing magnesium chloride and hydrogen.

Copper sulfate displacement by magnesium

Mg + CuSO₄ → MgSO₄ + Cu; magnesium displaces copper, turning the solution colorless and depositing brown copper.

Mnemonic for reactivity series

"Pond slime can make a zoo interesting – the long crinkly sort goes purple" (helps recall metal order).