Chapter 11: Chemical changes

What is a physical change?

No new substance formed, usually reversible. Example: melting ice, dissolving sugar.

What is a chemical change?

New substance formed, usually irreversible. Example: burning paper, rusting iron.

What is the difference between physical and chemical changes?

Physical: reversible, no new substance. Chemical: irreversible, new substance formed.

What are reactants?

Substances that undergo change in a reaction.

What are products?

New substances formed after the reaction.

What is a combination reaction?

Two or more substances combine to form one substance. Example: magnesium + oxygen \rightarrow magnesium oxide.

What is a decomposition reaction?

One substance breaks down into two or more substances. Example: calcium carbonate \rightarrow calcium oxide + carbon dioxide.

What type of energy change is combustion?

Exothermic (releases heat and light).

What type of energy change is photosynthesis?

Endothermic (absorbs light energy).

Define combustion.

Rapid reaction with oxygen producing heat and light.

Write the combustion equation for methane in words.

Methane + oxygen \rightarrow carbon dioxide + water.

Define thermal decomposition.

Breaking down of a compound using heat.

Write the decomposition of calcium carbonate in words.

Calcium carbonate \rightarrow calcium oxide + carbon dioxide.

What is oxidation?

A reaction with oxygen.

Write the word equation for rusting.

Iron + oxygen + water \rightarrow hydrated iron(III) oxide (rust).

What is neutralisation?

Reaction between an acid and an alkali to form salt and water.

Write an example of neutralisation in words.

Hydrochloric acid + sodium hydroxide \rightarrow sodium chloride + water.

Give one application of neutralisation.

Using antacids to relieve excess stomach acid.

State two properties of acids.

Sour taste, pH < 7, turns blue litmus red.

Give two examples of acids.

Hydrochloric acid, sulfuric acid.

What is produced when acid reacts with metal?

Salt + hydrogen gas.

How do you test for hydrogen gas?

Insert lighted splint \rightarrow ‘pop’ sound.

What is produced when acid reacts with carbonate?

Salt + carbon dioxide + water.

How do you test for carbon dioxide?

Bubble gas through limewater \rightarrow turns milky.

State two properties of alkalis.

Bitter taste, slippery, pH > 7, turns red litmus blue.

Give two examples of alkalis.

Sodium hydroxide, potassium hydroxide.

What does the pH scale measure?

Acidity and alkalinity (0–14).

What is neutral on the pH scale?

pH = 7

What happens to blue litmus in acid?

Turns red.

What happens to red litmus in alkali?

Turns blue.

Name four factors that cause chemical changes.

Mixing, heating, exposure to light, interaction with oxygen.

What is electroplating?

Using electric current to deposit a thin layer of metal on another object.

What chemical change happens in respiration?

Glucose + oxygen \rightarrow carbon dioxide + water + energy.

What chemical change happens in cooking?

Caramelisation, Maillard reaction.

What causes decay?

Decomposition by microorganisms.

What causes rusting?

Reaction of iron with oxygen and water.

Why is combustion important in daily life?

Provides energy by burning fuels.

Write the word equation for photosynthesis.

Carbon dioxide + water \rightarrow glucose + oxygen (light energy + chlorophyll).

Write the word equation for film photography (silver halide reaction).

Silver bromide \rightarrow silver + bromine (light).

Write the word equation for calcium carbonate decomposition.

Calcium carbonate \rightarrow calcium oxide + carbon dioxide.

Write the word equation for methane combustion.

Methane + oxygen \rightarrow carbon dioxide + water.

Write the word equation for magnesium and oxygen combination.

Magnesium + oxygen \rightarrow magnesium oxide.

Write the word equation for rusting.

Iron + oxygen + water \rightarrow hydrated iron(III) oxide (rust).