1. What is the most fundamental characteristic that defines a chemical reaction?
- A. The substances change their state of matter, such as from a liquid to a gas.
- B. The temperature of the mixture increases or decreases significantly.
- C. New substances with properties different from the original ones are formed.
- D. The original substances are simply mixed together without changing their identity.
2. Which of the following describes a physical change, rather than providing evidence of a chemical reaction?
- A. An iron nail rusting and turning reddish-brown.
- B. An antacid tablet fizzing and producing bubbles in water.
- C. A puddle of water evaporating on a hot day.
- D. Two liquids being mixed to form a yellow solid.
3. When baking soda is mixed with vinegar, the mixture begins to bubble and fizz. This observation suggests a chemical reaction has occurred because:
- A. the vinegar is dissolving the baking soda powder.
- B. a gas is being produced.
- C. the mixture is being stirred.
- D. the two substances have different densities.
4. A scientist is trying to determine if a chemical reaction took place. Which observation would be the LEAST reliable indicator on its own?
- A. The mixture changed from clear to a deep blue color.
- B. The mixture became slightly warmer after mixing.
- C. A solid material formed and settled out of two mixed liquids.
- D. Bubbles of gas were seen rising from the liquid.
5. A student mixes sand with water in a beaker. After a few minutes, the sand settles at the bottom. Why is this process NOT a chemical reaction?
- A. No new substance was formed.
- B. The process was reversible by evaporating the water.
- C. A solid was present at the beginning and the end.
- D. The beaker did not get hot or cold during the process.
6. When iron rusts, it combines with oxygen to form iron oxide. In this chemical reaction, what is the iron oxide?
- A. A reactant
- B. A product
- C. A physical mixture
- D. An element
7. When baking a cake, ingredients like flour, sugar, and eggs are mixed and heated, resulting in a cake with very different properties. What role do the flour, sugar, and eggs play in this process?
- A. They are the products.
- B. They are the catalysts.
- C. They are the physical means.
- D. They are the reactants.
8. If you mix sand and iron filings, you can use a magnet to separate them. If you heat the mixture until they react to form a new, non-magnetic substance, what have you created?
- A. A new reactant
- B. A simple mixture
- C. A chemical product
- D. A physical solution
9. In any chemical reaction, what is the scientific term for the starting substances that undergo a transformation?
- A. Products
- B. Reactants
- C. Catalysts
- D. Mixtures
10. Which statement best describes the fundamental process of a chemical reaction?
- A. Reactants are physically combined and can be easily separated again.
- B. Products spontaneously break down to re-form the original reactants.
- C. Reactants are consumed and chemically transformed into new substances called products.
- D. Reactants and products are identical, but their physical state changes.