3.2

Equations

10 flashcards to master Equations

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Definition Flip

Define relative atomic mass (Ar).

Answer Flip

Ar is the average mass of the isotopes of an element compared to 1/12th of the mass of an atom of carbon-12.

Example: the Ar of chlorine is approximately 35.5, considering the abundance of chlorine-35 and chlorine-37.
Definition Flip

Define relative molecular mass (Mr).

Answer Flip

Mr is the sum of the relative atomic masses of the atoms in a molecule.

Example: the Mr of water (H₂O) is (2 x Ar of H) + Ar of O = (2 x 1) + 16 = 18.
Definition Flip

Define relative formula mass.

Answer Flip

The relative formula mass is used for ionic compounds. It is calculated by summing the relative atomic masses of each element in the formula.

Example: the relative formula mass of NaCl is Ar(Na) + Ar(Cl) = 23 + 35.5 = 58.5.
Key Concept Flip

What state symbols are commonly used in chemical equations, and what do they represent?

Answer Flip

(s) - solid, (aq) - aqueous (dissolved in water), (l) - liquid, (g) - gas. All state symbols must be correct in chemical equations. For

Example: NaCl(s) + H₂O(l) → Na⁺(aq) + Cl⁻(aq).
Key Concept Flip

In the reaction 2HCl + CaCO₃ → CaCl₂ + H₂O + CO₂, if 0.0100 moles of HCl react, how many moles of CO₂ are produced?

Answer Flip

According to the balanced equation, 2 moles of HCl produce 1 mole of CO₂. Therefore, 0.0100 moles of HCl produce 0.0100 / 2 = 0.00500 moles of CO₂.

Key Concept Flip

In the reaction 2HCl + CaCO₃ → CaCl₂ + H₂O + CO₂, if 0.0100 moles of HCl react, calculate the volume of CO₂ produced at room temperature and pressure where 1 mole of gas occupies 24000 cm³.

Answer Flip

First find moles of CO₂ produced, in this case 0.00500. Volume of CO₂ = 0.00500 x 24000 = 120 cm³.

Key Concept Flip

Give an example of a reaction that causes nitrogen oxides to form.

Answer Flip

Nitrogen and oxygen from the air react at high temperatures, such as in a car engine, to form nitrogen oxides.

Key Concept Flip

What are the negative effects of producing nitrogen oxides?

Answer Flip

Nitrogen oxides can cause acid rain and respiratory problems.

Definition Flip

What type of reaction is the breakdown of a compound by heating?

Answer Flip

This is called thermal decomposition. An example is the thermal decomposition of calcium carbonate into calcium oxide and carbon dioxide.

Key Concept Flip

Describe a test for ammonia gas.

Answer Flip

Add aqueous sodium hydroxide/ add damp red litmus paper. If ammonia is present, the litmus paper will turn blue.

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3.1 Formulae 3.3 Calculations

Key Questions: Equations

Define relative atomic mass (Ar).

Ar is the average mass of the isotopes of an element compared to 1/12th of the mass of an atom of carbon-12.

Example: the Ar of chlorine is approximately 35.5, considering the abundance of chlorine-35 and chlorine-37.
Define relative molecular mass (Mr).

Mr is the sum of the relative atomic masses of the atoms in a molecule.

Example: the Mr of water (H₂O) is (2 x Ar of H) + Ar of O = (2 x 1) + 16 = 18.
Define relative formula mass.

The relative formula mass is used for ionic compounds. It is calculated by summing the relative atomic masses of each element in the formula.

Example: the relative formula mass of NaCl is Ar(Na) + Ar(Cl) = 23 + 35.5 = 58.5.
What type of reaction is the breakdown of a compound by heating?

This is called thermal decomposition. An example is the thermal decomposition of calcium carbonate into calcium oxide and carbon dioxide.

About Equations (3.2)

These 10 flashcards cover everything you need to know about Equations for your Cambridge IGCSE Chemistry (0620) exam. Each card is designed based on the official syllabus requirements.

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