Year 8 Chemical Reactions

Comprehensive vocabulary flashcards covering chemical and physical changes, reaction types, naming conventions, gas tests, the reactivity series, and explosions from the course booklet.

Physical Change

A change of state where no new substance is formed, which is usually easily reversed (such as upon cooling) and typically involves very little heat being released or absorbed.

Chemical Change

A process resulting from a chemical reaction where bonds in the reactants break and atoms rearrange to form one or more new substances; it is usually not easily reversed and often involves a large release or absorption of heat or light.

Physical Property

An observable or measurable characteristic of a substance that does not alter its chemical composition or create a new substance.

Chemical Property

A characteristic that describes how a substance interacts chemically with other substances to undergo a chemical change and form new products.

Reactants

The starting chemical substances shown on the left-hand side of a chemical equation that undergo change during a chemical reaction.

Products

The new chemical substances formed on the right-hand side of a chemical equation as a result of a chemical reaction.

Word Equation

A chemical representation using the names of substances with three parts: the names of the reactants, an arrow indicating chemical change, and the names of the products, without representing atomic quantities.

Chemical Equation

A representation of a chemical reaction using chemical symbols and molecular formulae to show reactants and products, which can be balanced (such as $2Cu + O_2 \rightarrow 2CuO$).

General Equation

A broad, standardised equation pattern describing a specific category of reaction, such as $\text{metal} + \text{acid} \rightarrow \text{salt} + \text{hydrogen}$.

Salt

A compound formed during an acid reaction when the hydrogen of the acid is replaced by a metal or positive ion.

Chlorides

A family of salts produced when metals or bases react with hydrochloric acid ($HCl$).

Sulphates

A family of salts produced when metals or bases react with sulphuric acid ($H_2SO_4$).

Nitrates

A family of salts produced when metals or bases react with nitric acid ($HNO_3$).

Precipitation

A type of chemical reaction where two solutions are mixed together and react to form an insoluble solid that falls out of solution.

Precipitate

An insoluble solid compound formed during a precipitation reaction, such as white $AgCl$, white $BaSO_4$, bright yellow $PbI_2$, reddish-brown $Fe(OH)_3$, or blue $Cu(OH)_2$.

Combustion

The scientific term for burning; an oxidation reaction where a substance reacts rapidly with oxygen to produce heat and light energy.

Fire Triangle

The model representing the three essential components required for combustion to occur: fuel, oxygen, and heat.

Neutralisation

A chemical reaction between an acid and a base that produces a salt and water, occurring because $H^+$ from the acid combines with $OH^-$ from the base to form neutral $H_2O$.

Acid

A substance containing replaceable hydrogen (such as $HCl$, $HNO_3$, $H_2SO_4$, or $H_3PO_4$) that has a pH less than 7 and neutralises bases to form salts.

Base

A chemical substance, such as a metal oxide, metal hydroxide, or metal carbonate, that reacts with an acid to produce a salt and water.

Alkali

A water-soluble base that produces hydroxide ions in aqueous solution and has a pH greater than 7.

Oxides

Compounds formed when elements react with oxygen, often produced when metals or nonmetals burn in air.

Hydroxides

Compounds containing the hydroxide group ($OH^-$), formed by the reaction of reactive metals with water or the reaction of acids with alkalis.

Carbonates

Compounds containing the carbonate group (such as $CaCO_3$ in limestone or marble chips) that react with acids to yield a salt, water, and carbon dioxide gas.

Saturated Solution

A chemical solution in which no more solute (such as excess base or metal oxide) can dissolve into the solvent at a given temperature.

Crystallisation Point

The point during the gentle heating of a salt solution when small crystals begin to form on the inside wall of the evaporating dish just above the liquid level.

Pop Test

The standard laboratory test for hydrogen gas, where an inverted test tube containing the gas makes a distinctive 'pop' sound upon introducing a lighted wooden splint as it reacts with oxygen to make water.

Glowing Splint Test

The laboratory test for oxygen gas, where a glowing wooden splint blown free of flames relights when inserted into a gas-filled tube because oxygen supports combustion.

Limewater Test

The laboratory test for carbon dioxide gas, where bubbling $CO_2$ through limewater (calcium hydroxide) turns it cloudy or milky due to the formation of an insoluble calcium carbonate precipitate.

Reactivity Series

A ranked progression of metals based on how readily they lose electrons and react with substances like water, oxygen, and acids, ranging from potassium at the top to platinum at the bottom.

Explosion

Defined by J. Reed as a sudden, violent conversion of potential energy into work, which transfers to its surroundings as a rapid rise in pressure called a blast wave or shockwave.

Gunpowder

The earliest explosive, invented in China, consisting of a mixture of potassium nitrate, charcoal, and sulfur that produces copious amounts of smoke.

Guncotton

A smokeless form of nitrocellulose first produced in 1833 by Henry Broconnot using cotton treated with nitric acid, and later optimized in 1846 by Christian Friedrich Schonbein and F. J. Otto using nitric and sulfuric acids.

Dynamite

A safer explosive synthesized in 1867 by Alfred Nobel by combining volatile nitroglycerin with diatomaceous earth and sodium carbonate.

Nuclear Explosion

An explosion caused by nuclear fusion or nuclear fission, where mass lost ($m$) is converted into released energy ($E$) according to $E = mc^2$, with the speed of light $c = 3.0 \times 10^8\,m/s$.

Chemical Explosion

An explosion involving a rapid, violent oxidation (burning), decomposition, or combination reaction that rapidly releases large amounts of gas and heat.

Physical Explosion

An explosion occurring without a chemical or nuclear reaction, most frequently caused by the rupture or bursting of a vessel containing liquid or gas under high pressure.