Master Chemical Reactions and Equations with Chemistry review games.
This unit covers balancing equations, reaction types and conservation of mass — essential concepts for Chemistry. Use our interactive study games to test your understanding, or review questions in traditional format below.
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This unit covers balancing equations, reaction types and conservation of mass — essential concepts for Chemistry. Use our interactive study games to test your understanding, or review questions in traditional format below.
Key Concepts Breakdown
1 Balancing Equations
Students must be able to balance chemical equations by adjusting coefficients so that the number of each type of atom is equal on both sides. Subscripts cannot be changed — only coefficients. This skill is tested directly and also required for stoichiometry problems.
Key Points
- Coefficients multiply the entire formula; subscripts are fixed and define the compound
- Balance one element at a time; save pure elements (O₂, H₂) for last
- A balanced equation must have equal atoms of each element on both sides
- The simplest whole-number ratio of coefficients is the correct form
Balance: H₂ + O₂ → H₂O
Start with hydrogen: 2 H on the left, 2 H on the right — balanced. Oxygen: 2 on the left, 1 on the right — not balanced. Place a coefficient of 2 in front of H₂O, giving 2 O on the right, then fix hydrogen by placing 2 in front of H₂. Final balanced equation: 2H₂ + O₂ → 2H₂O.
2 Reaction Types
Students must identify and classify chemical reactions as synthesis, decomposition, single replacement, double replacement, or combustion based on the pattern of reactants and products. Exams require both recognizing a type from an equation and predicting products given a type. Combustion of hydrocarbons always produces CO₂ and H₂O.
Key Points
- Synthesis: A + B → AB (two or more substances combine into one)
- Decomposition: AB → A + B (one substance breaks into two or more)
- Single replacement: A + BC → AC + B (one element displaces another in a compound)
- Double replacement: AB + CD → AD + CB (ions of two compounds swap partners); Combustion: hydrocarbon + O₂ → CO₂ + H₂O
Classify and complete: Zn + HCl → ?
Zinc (a pure element) reacts with hydrochloric acid (a compound), so this is a single replacement reaction. Zinc displaces hydrogen from HCl, forming zinc chloride and hydrogen gas. The completed, balanced equation is: Zn + 2HCl → ZnCl₂ + H₂.
3 Conservation Of Mass
The Law of Conservation of Mass states that mass is neither created nor destroyed in a chemical reaction — the total mass of reactants equals the total mass of products. This is the theoretical reason why equations must be balanced. Exams test this both conceptually and with calculation-based questions.
Key Points
- Total mass of reactants = total mass of products in every chemical reaction
- Atoms are rearranged, not created or destroyed, during a reaction
- If 10 g of reactants are used and 7 g of one product forms, the other product must account for the remaining 3 g
- A balanced equation is the symbolic demonstration of conservation of mass
2.0 g of hydrogen reacts completely with 16.0 g of oxygen. What mass of water is produced?
According to the Law of Conservation of Mass, the total mass of products must equal the total mass of reactants. Add the masses of the reactants: 2.0 g + 16.0 g = 18.0 g. Therefore, 18.0 g of water is produced — no mass is gained or lost.
Questions, answered.
What is Chemical Reactions and Equations?
Chemical Reactions and Equations is Unit 4 of Chemistry, covering balancing equations, reaction types and conservation of mass.
How to study for Chemistry Unit 4?
Start with the Quick Summary above, review the Key Concepts, then test yourself with our interactive study games. Aim for 80%+ accuracy before moving on.
How many questions are in this unit?
This unit has 27+ review questions across 5 different game modes.