Last updated on Sep 21, 2026

Measurement, Mass & Equations (AQA GCSE Chemistry Combined Science): Flashcards

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Conservation of Mass & Balanced Chemical Equations

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Law of conservation of mass

Total mass of reactants = total mass of products

Why mass is conserved in reactions

No atoms created or destroyed, just rearranged

Balanced chemical equation meaning

Same number of atoms of each element on both sides

Coefficients in chemical equations

Numbers in front of formulas to balance atoms

Purpose of balancing equations

To reflect conservation of mass

First step to balance an equation

Write the unbalanced equation

What to adjust when balancing equations

Coefficients (numbers in front of formulas)

Sum of $M_r$ in balanced equations

Sum of $M_r$ of reactants = sum of $M_r$ of products

Relative formula mass ( $M_r$ )

Total mass of all atoms in a compound

How to calculate $M_r$

Add up $A_r$ of all elements in the compound

Balanced equation: $N_2$ + ? $H_2$ → ? $NH_3$

$N_2 + 3H_2 → 2NH_3$

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