GCSE Chemistry revision

Mass changes when a reactant or product is a gas

Chemical measurements, conservation of mass and the quantitative interpretation of chemical equations

AQA 4.3.1.3 Foundation & Higher

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Gas Escaping (Apparent Mass Loss): In an open system, if a gas is produced, gas particles escape into the atmosphere, causing a measured decrease in mass even though total matter is conserved in accordance with the particle model.
Gas Reacting (Apparent Mass Gain): When a solid reacts with a gas from the air (such as magnesium reacting with oxygen), gas particles enter the open reaction vessel to combine with solid particles, resulting in a measured increase in total mass.

1. Mass Changes in Non-Enclosed Systems AQA

Gas Escaping (Apparent Mass Loss): In an open system, if a gas is produced, gas particles escape into the atmosphere, causing a measured decrease in mass even though total matter is conserved in accordance with the particle model.
Gas Reacting (Apparent Mass Gain): When a solid reacts with a gas from the air (such as magnesium reacting with oxygen), gas particles enter the open reaction vessel to combine with solid particles, resulting in a measured increase in total mass.

Word and Symbol Equations with State Symbols: Reactants and products are represented using word or balanced symbol equations that include state symbols: (s) for solid, (l) for liquid, (g) for gas, and (aq) for aqueous solution.
Ionic Equations and Equation Deduction: Ionic equations simplify reactions by showing only the reacting ions that change state while omitting spectator ions; balanced symbol equations are deduced by matching atomic counts and applying appropriate state symbols.

2. Constructing Word, Symbol, and Ionic Equations AQA

Word and Symbol Equations with State Symbols: Reactants and products are represented using word or balanced symbol equations that include state symbols: (s) for solid, (l) for liquid, (g) for gas, and (aq) for aqueous solution.
Ionic Equations and Equation Deduction: Ionic equations simplify reactions by showing only the reacting ions that change state while omitting spectator ions; balanced symbol equations are deduced by matching atomic counts and applying appropriate state symbols.

Haber Process Equation: The industrial production of ammonia from nitrogen and hydrogen gas is a reversible reaction written as:
N₂_(g) + 3H₂_(g) ⇌ 2NH₃_(g)
Contact Process Equation: The reversible conversion of sulfur dioxide and oxygen into sulfur trioxide during sulfuric acid manufacture is written as:
2SO₂_(g) + O₂_(g) ⇌ 2SO₃_(g)

3. Key Industrial Symbol Equations AQA

Haber Process Equation: The industrial production of ammonia from nitrogen and hydrogen gas is a reversible reaction written as:
N₂_(g) + 3H₂_(g) ⇌ 2NH₃_(g)
Contact Process Equation: The reversible conversion of sulfur dioxide and oxygen into sulfur trioxide during sulfuric acid manufacture is written as:
2SO₂_(g) + O₂_(g) ⇌ 2SO₃_(g)