Across
- 2. A substance that speeds up a chemical reaction
- 5. A positively charged particle in the nucleus
- 6. A combination of substances that are not chemically bonded.
- 7. A measure of how acidic or basic a solution is.
- 8. A pure substance that cannot be broken down into simpler substances by chemical means
- 9. The most abundant element in the Earth's atmosphere.
Down
- 1. A negatively charged particle orbiting the nucleus
- 3. When a solid turns directly into a gas.
- 4. A reaction that releases heat to its surroundings.