Year 8 - Science
Conservation of mass and balanced symbol equations
Understanding chemical reactions
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This pupil-friendly study guide includes a unit summary, clear notes, common mistakes, and quick questions with answers.
Unit Summary
This unit covers the conservation of mass in changes of state and chemical reactions, including atom rearrangement. It also focuses on representing reactions with formulae and equations, exploring combustion, decomposition, and displacement, and distinguishing chemical from physical changes.
Lesson Summary
You will learn to explain the conservation of mass and write balanced chemical equations to show how the atoms of reactants in a chemical reaction are rearranged to form products.
Key Notes
- The mass of the products in a chemical reaction is the same as the mass of the reactants.
- Word equations are a simple way of describing chemical reactions.
- Chemical formulae represent the numbers of each type of atoms in a reactant or product.
- Chemical equations represent how the atoms in the reactants rearrange to form the products.
- The arrow in a chemical equation represents the words 'changes into'.
Vocabulary To Learn
- chemical formula: represents a substance using element symbols and the number / ratio of atoms of each element in the substance.
- word equation: is a way of describing a reaction using the chemical names of the reactants and products.
- balanced symbol equation: describes a reaction using a symbol equation with coefficients, which ensure there are equal numbers of atoms of each element on both sides of the symbol equation.
- coefficient: is the number placed in front of a chemical formula to balance an equation; it multiplies all the atoms in the formula and shows the ratio of substances in a reaction.
Common Mistakes To Avoid
- Pupils get confused with what numbers can be changed, many of them try to change the subscript numbers in formulae to balance equations.
3 Quick Questions (With Answers)
1. Explain the scientific idea in this lesson using two key points.
The mass of the products in a chemical reaction is the same as the mass of the reactants. Word equations are a simple way of describing chemical reactions.
2. Define this scientific word and use it in context. 'chemical formula'
represents a substance using element symbols and the number / ratio of atoms of each element in the substance. Include the word in a full scientific explanation, not as a single label.
3. Correct this common scientific misunderstanding.
Mistake: Pupils get confused with what numbers can be changed, many of them try to change the subscript numbers in formulae to balance equations. Correction: Use the layout modelled in the slides to go through the examples using the 'circled method' and tell pupils that when adding more of a substance they must add all elements in the substance, e.g. 2MgO = (MgO)(MgO).
More Lessons In This Unit
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