This cheat sheet covers the most common inorganic reaction patterns used in high school chemistry. Students need these patterns to predict products, write balanced equations, and recognize evidence of chemical change. It is especially useful when reviewing reaction classification, solubility rules, acids and bases, and oxidation-reduction reactions.
The core idea is that many inorganic reactions follow predictable templates such as , , or . Net ionic equations focus on the particles that actually react, often showing formation of a precipitate, water, or gas. Redox reactions are identified by changes in oxidation number, while acid-base reactions usually transfer and form water or a salt.
Key Facts
- A synthesis reaction combines simpler substances into one product, following the pattern .
- A decomposition reaction breaks one compound into simpler substances, following the pattern .
- A single replacement reaction follows only if element is more reactive than element .
- A double replacement reaction follows when a precipitate, water, or gas forms.
- A combustion reaction of a hydrocarbon produces carbon dioxide and water, such as .
- An acid-base neutralization often follows , with the net ionic equation .
- A precipitation reaction occurs when aqueous ions form an insoluble solid, such as .
- A redox reaction occurs when oxidation numbers change, with oxidation meaning loss of electrons and reduction meaning gain of electrons.
Vocabulary
- Synthesis reaction
- A reaction in which two or more reactants combine to form one main product.
- Decomposition reaction
- A reaction in which one compound breaks apart into two or more simpler products.
- Precipitate
- An insoluble solid that forms when ions in aqueous solution combine.
- Net ionic equation
- An equation that shows only the ions or molecules that directly participate in the chemical change.
- Oxidation number
- A bookkeeping charge assigned to an atom to track electron transfer in redox reactions.
- Spectator ion
- An ion that remains unchanged in solution and does not appear in the net ionic equation.
Common Mistakes to Avoid
- Forgetting to balance the equation is wrong because reaction type does not replace conservation of atoms. After predicting products, adjust coefficients so each element has the same number of atoms on both sides.
- Writing double replacement products without checking solubility is wrong because many ion swaps have no visible reaction. A precipitate forms only when one product is insoluble according to solubility rules.
- Treating all single replacement reactions as automatic is wrong because activity matters. The free element must be more reactive than the element it replaces.
- Confusing subscripts with coefficients is wrong because changing a subscript changes the compound itself. Balance equations by changing coefficients such as , not by changing into a different formula.
- Calling every reaction with oxygen combustion is wrong because combustion usually means rapid reaction with that releases energy and forms oxides. For hydrocarbons, the expected products are and .
Practice Questions
- 1 Balance and classify this reaction: .
- 2 Predict the products and write the balanced equation for .
- 3 Balance the combustion reaction .
- 4 Explain how you can tell whether is a redox reaction without doing a full calculation.