Summary
Stoichiometry involves calculating the quantities of reactants and products in chemical reactions.
- Molecular Formula — shows the actual number of atoms of each element in a molecule. Example: H2O represents two hydrogen atoms and one oxygen atom.
- Relative Formula Mass (Mr) — the sum of the relative atomic masses of all atoms in a formula. Example: The Mr of HNO3 is 63.
- Balanced Equation — an equation where the number of atoms for each element is the same on both sides. Example: H2 + Cl2 ➔ 2HCl.
Exam Tips
Key Definitions to Remember
- Molecular Formula
- Relative Formula Mass (Mr)
- Balanced Equation
Common Confusions
- Confusing molecular formulas with empirical formulas
- Miscalculating the relative formula mass by not including all atoms
Typical Exam Questions
- What is the balanced equation for the reaction between hydrogen and chlorine? H2 + Cl2 ➔ 2HCl
- What is the relative formula mass of HNO3? 63
- Which mass of sulfur is present in 160 g of copper(II) sulfate? 32g
What Examiners Usually Test
- Ability to balance chemical equations
- Calculating relative formula masses
- Understanding the composition of compounds