Mass in a chemical reaction
I can use conservation of mass and relative formula masses to predict the mass of unknown products or reactants.
- Year 10
- AQA
Mass in a chemical reaction
I can use conservation of mass and relative formula masses to predict the mass of unknown products or reactants.
Lesson details
Key learning points
- In a chemical reaction, the atoms in reactants are rearranged and are the same atoms that are in the products.
- The mass of products in a chemical reaction is equal to the mass of the reactants.
- The sum of the RFM of the reactants equals the sum of the RFM of the products, taking account of balancing coefficients.
Keywords
Balanced symbol equation - A balanced symbol equation represents a chemical reaction using symbols and coefficients to ensure that the number of atoms of each element is equal on both sides of the equation.
Conservation of mass - Conservation of mass means the total mass of the starting reactants equals the total mass of the products formed.
Relative formula mass - The relative formula mass (RFM or Mᵣ) of a substance is the sum of the relative atomic masses of all the atoms in its formula.
Coefficient - A 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 misconception
Pupils struggle to recall the order of steps required to mathematically process the available information in order to answer the question.
Colour-coding the steps can help pupils remember how many steps are involved. Much practice and perseverance is needed to create and maintain the memory pathway of the mathematical processing.
Equipment
Licence
Lesson video
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Prior knowledge starter quiz
6 Questions
Q1.Given the relative atomic masses (Ar): C (12), O (16)
Calculate the relative molecular mass (Mr) of carbon dioxide (CO₂).
Q2.What does the conservation of mass in a chemical reaction imply?
Q3.If 20g of sodium reacts fully with 15g of chlorine, how much sodium chloride is produced?
Q4.For the equation __ N₂ + __ H₂ → __ NH₃, select the correct coefficients to balance it.
Q5.What does the equation 2H₂ + O₂ → 2H₂O tell us?
Q6.Given the relative atomic mass values (Ar): H (1), S (32), O (16)
Calculate the relative formula mass (Mr) of sulfuric acid.
Assessment exit quiz
6 Questions
Q1.Match the following terms with their correct definitions:
