Chemical Reactions and Equations – Chapter 1 Review

These flashcards cover the key concepts, definitions, examples, and equations from the Chapter 1 lecture on Chemical Reactions and Equations, including reaction indicators, balancing methods, types of reactions, energy changes, corrosion, and everyday applications.

What four common observations indicate that a chemical reaction has taken place?

Change in state, change in colour, evolution of a gas, and change in temperature.

What is meant by a chemical reaction?

A process in which one or more substances (reactants) are converted into new substances (products) with different identities and properties.

In a word-equation, where are reactants and products written?

Reactants are written on the left-hand side (LHS) and products on the right-hand side (RHS) of the arrow.

What is a skeletal chemical equation?

An unbalanced equation that uses chemical formulae but does not show equal numbers of atoms of each element on both sides.

State the Law of Conservation of Mass.

Mass can neither be created nor destroyed in a chemical reaction; the total mass of reactants equals the total mass of products.

Why must a chemical equation be balanced?

To satisfy the Law of Conservation of Mass by ensuring the same number of atoms of each element on both sides of the equation.

Which method is commonly used to balance chemical equations in school-level chemistry?

The hit-and-trial (trial-and-error) method.

Why is a magnesium ribbon cleaned before burning in air?

To remove the protective layer of basic magnesium carbonate so that the metal can burn readily.

Give the symbols for solid, liquid, gas and aqueous states used in chemical equations.

(s) solid, (l) liquid, (g) gas, (aq) aqueous (dissolved in water).

How are special reaction conditions such as temperature or catalyst shown in a chemical equation?

They are written above or below the reaction arrow.

Define a combination reaction.

A reaction in which two or more substances combine to form a single product.

Write the combination reaction equation for quick lime with water.

CaO(s) + H₂O(l) → Ca(OH)₂(aq) + heat.

What is an exothermic reaction?

A reaction that releases heat energy to the surroundings.

Give an everyday biological example of an exothermic reaction.

Respiration: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy.

Define an endothermic reaction.

A reaction that absorbs energy from the surroundings, usually in the form of heat, light or electricity.

How does slaked lime give walls a shiny finish after whitewashing?

Ca(OH)₂ reacts slowly with CO₂ in air forming a thin layer of CaCO₃, which is shiny.

What is a decomposition reaction?

A reaction in which a single compound breaks down into two or more simpler substances.

What term is used for decomposition driven by heat?

Thermal decomposition.

Give the thermal decomposition equation of calcium carbonate.

CaCO₃(s) → CaO(s) + CO₂(g).

What kind of decomposition is the splitting of water by electricity?

Electrolytic (electrolytic decomposition).

Why is twice as much hydrogen collected as oxygen during electrolysis of water?

Because water contains twice as many hydrogen atoms as oxygen atoms; the balanced equation is 2H₂O → 2H₂ + O₂.

Write the photolytic decomposition equation of silver chloride.

2AgCl(s) ⟶ 2Ag(s) + Cl₂(g) (in sunlight).

Define a displacement reaction.

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

Provide an example of a displacement reaction using iron and copper sulphate.

Fe(s) + CuSO₄(aq) → FeSO₄(aq) + Cu(s).

What is a double displacement reaction?

A reaction in which two compounds exchange ions to form two new compounds.

Define a precipitation reaction.

A reaction that forms an insoluble solid (precipitate) when two aqueous solutions are mixed.

Give the double displacement equation that produces a white precipitate of barium sulphate.

Na₂SO₄(aq) + BaCl₂(aq) → BaSO₄(s) + 2NaCl(aq).

What is oxidation in terms of oxygen and hydrogen transfer?

Gain of oxygen or loss of hydrogen by a substance.

Define reduction in simple terms.

Loss of oxygen or gain of hydrogen by a substance.

What is a redox reaction?

A reaction in which oxidation and reduction occur simultaneously.

In the reaction CuO + H₂ → Cu + H₂O, which substance is oxidised and which is reduced?

H₂ is oxidised to H₂O (gains oxygen); CuO is reduced to Cu (loses oxygen).

What is corrosion?

The gradual destruction of metals by reaction with moisture, air or other chemicals, forming undesirable compounds on their surfaces.

What common name is given to the corrosion of iron?

Rusting.

Define rancidity.

Oxidation of fats and oils that produces unpleasant taste and smell.

Why are bags of potato chips flushed with nitrogen?

To displace oxygen and slow down oxidation, preventing rancidity.

State one way to slow down rancidity in household food storage.

Keep fatty foods in airtight containers to limit exposure to oxygen.

Why is paint applied to iron articles?

To form a protective barrier that prevents moisture and oxygen from reaching the metal surface, thereby reducing corrosion.

How are exothermic and endothermic reactions different?

Exothermic reactions release energy (usually heat) whereas endothermic reactions absorb energy.

Explain why decomposition reactions are considered the opposite of combination reactions.

Combination reactions form a single product from multiple reactants, while decomposition reactions break a single reactant into multiple products.

Write the balanced equation for combustion of methane and classify the reaction.

CH₄ + 2O₂ → CO₂ + 2H₂O + heat; it is a combination and exothermic reaction.

Differentiate between displacement and double displacement reactions with respect to ion exchange.

Displacement reactions involve one element replacing another in a compound, whereas double displacement reactions involve mutual exchange of ions between two compounds.

What industrial use does quick lime (CaO) derived from thermal decomposition of limestone have?

It is a key ingredient in the manufacture of cement.

What does the term ‘balanced chemical equation’ mean?

An equation that shows equal numbers of atoms of each element on both the reactant and product sides.

Name the method commonly used to add slaked lime to walls and the chemical formula of the final shiny compound formed.

Whitewashing; the shiny compound formed is CaCO₃.