# ACT Chemistry Core Concepts Review
While the ACT Science section tests data interpretation skills rather than content knowledge, having a basic understanding of chemistry concepts helps you read passages faster and answer questions more confidently.
1. Atomic Structure
- Atoms: protons (+), neutrons (0), electrons (−)
- Atomic number = protons; mass number = protons + neutrons
- Isotopes: same element, different neutrons
- Electron configuration determines chemical properties
2. Chemical Reactions
- Reactants → Products
- Balanced equations conserve mass
- Types: synthesis, decomposition, combustion, acid-base, redox
- Catalysts speed up reactions without being consumed
3. Acids and Bases
- Acids: pH < 7; donate H⁺
- Bases: pH > 7; accept H⁺
- Neutral: pH = 7
- Neutralisation: acid + base → salt + water
- Strong acids/bases fully dissociate; weak ones partially
4. Solutions and Concentration
- Concentration = amount of solute per volume of solution
- Solubility depends on temperature (usually increases for solids)
- Saturated solution: maximum solute dissolved
- Like dissolves like (polar in polar, nonpolar in nonpolar)
5. Gas Laws
- Boyle's: (T fixed)
- Charles's: (P fixed)
- Combined:
- Higher temperature → faster particles → higher pressure (fixed V)
6. Energy in Reactions
- Exothermic: releases energy (feels hot; )
- Endothermic: absorbs energy (feels cold; )
- Activation energy: minimum energy to start a reaction
7. Rate of Reaction
- Faster with: higher temperature, higher concentration, smaller particles, catalyst
- Measured by: gas volume, mass change, colour change, time
8. The Periodic Table
- Groups (columns): similar properties
- Periods (rows): same number of electron shells
- Metals on left; non-metals on right
- Trends: atomic radius, electronegativity, ionisation energy
9. Practice Questions
- An ACT passage mentions pH values of 2, 7, and 12. Which is acidic, neutral, and basic?
- A gas is heated in a sealed container. What happens to the pressure?
- A reaction produces bubbles faster when heated. Why?
- What does it mean if a reaction is described as "exothermic"?
- Two metals are placed in acid. One reacts vigorously, the other doesn't. What explains this?
Want to check your answers and get step-by-step solutions?
10. ACT Tips
- You don't need to memorize the periodic table — it may be provided
- Focus on understanding concepts, not calculations
- Most ACT chemistry questions can be answered from the passage alone
- Background knowledge helps with speed and confidence