Chemical Reactions Practice
Separate what you observe from what you infer. When balancing, change coefficients rather than the formula of a compound.
Learning objective
A printable worksheet on evidence of reaction, equations, particles and conservation of mass.
Questions
1. Give two observations that may suggest a chemical reaction, and explain why each needs context.
2. Count atoms in 2Ca(OH)2.
3. Why must the total number of each type of atom be the same before and after a reaction?
4. A student changes H2O to H2O2 while balancing. Explain the error.
Answer section
- 1. Examples include gas, temperature change or precipitate, but trapped air or colour mixing can mislead.
- 2. Two calcium, four oxygen and four hydrogen atoms.
- 3. Atoms are rearranged, not created or destroyed in the reaction model.
- 4. Changing a subscript changes the substance; use coefficients to count more particles.
Check your method: An answer is stronger when the working, unit, diagram or explanation makes the choice visible.