MISA - Maryland Integrated Science Assessment Properties of Chemical Reactions Questions and Answers — Questions and Answers
Question 1: A student mixes two clear, colorless liquids in a beaker. They observe the formation of a white solid and notice the beaker feels warm to the touch. Which statement best explains these observations?
- A physical change occurred, causing one liquid to freeze.
- The liquids were contaminated, resulting in a precipitate.
- A chemical reaction occurred, indicated by the formation of a precipitate and a change in temperature. (Correct answer)
- The beaker absorbed heat from the room, causing a solid to form.
Correct answer: A chemical reaction occurred, indicated by the formation of a precipitate and a change in temperature.
The formation of a new substance with different properties (a solid precipitate from two liquids) and the release of energy as heat (an exothermic reaction) are two classic indicators that a chemical reaction has taken place.
Question 2: In a closed system, 22 grams of reactant X are completely reacted with 8 grams of reactant Y. According to the Law of Conservation of Mass, what is the expected total mass of the products?
- Less than 30 grams if a gas is produced.
- 30 grams. (Correct answer)
- More than 30 grams if the reaction is exothermic.
- 14 grams.
Correct answer: 30 grams.
The Law of Conservation of Mass states that in a closed system, mass is neither created nor destroyed. Therefore, the total mass of the reactants must equal the total mass of the products. In this case, 22 g + 8 g = 30 g.
Question 3: A student wants to increase the rate of reaction between a solid lump of calcium carbonate and a hydrochloric acid solution. Which of the following actions would be LEAST effective at increasing the reaction rate?
- Crushing the lump of calcium carbonate into a powder.
- Gently warming the hydrochloric acid solution.
- Decreasing the concentration of the hydrochloric acid solution. (Correct answer)
- Stirring the mixture continuously.
Correct answer: Decreasing the concentration of the hydrochloric acid solution.
Decreasing the concentration of a reactant reduces the number of reactant particles in a given volume, which leads to fewer collisions per unit of time and therefore slows down the reaction rate. Increasing surface area (crushing), increasing temperature, and agitating the mixture all increase the reaction rate.
Question 4: The chemical equation for the combustion of methane is: CH₄ + 2 O₂ → CO₂ + 2 H₂O. In this reaction, which of the following are the reactants?
- CO₂ and H₂O
- CH₄ and O₂ (Correct answer)
- CH₄ and CO₂
- O₂ and H₂O
Correct answer: CH₄ and O₂
In a chemical equation, the substances written on the left side of the reaction arrow (→) are the reactants, which are the starting materials. The substances on the right side are the products. Therefore, methane (CH₄) and oxygen (O₂) are the reactants.
Question 5: An instant cold pack is activated by breaking an inner pouch, allowing two substances to mix. The pack quickly becomes very cold. This is an example of what type of process?
- An exothermic reaction
- A combustion reaction
- A physical change
- An endothermic reaction (Correct answer)
Correct answer: An endothermic reaction
An endothermic reaction is a process that absorbs heat from its surroundings. This absorption of heat causes the temperature of the surroundings (the pack itself) to decrease, making it feel cold.
Question 6: The chemical reaction 2 H₂O₂ → 2 H₂O + O₂ shows hydrogen peroxide changing into water and oxygen gas. How is this type of reaction best classified?
- Synthesis
- Decomposition (Correct answer)
- Single-replacement
- Double-replacement
Correct answer: Decomposition
A decomposition reaction occurs when a single, more complex compound breaks down into two or more simpler substances. In this case, hydrogen peroxide (H₂O₂) breaks down into water (H₂O) and oxygen (O₂).
MISA - Maryland Integrated Science Assessment Properties of Chemical Reactions Questions and Answers
A student mixes two clear, colorless liquids in a beaker.
They observe the formation of a white solid and notice the beaker feels warm to the touch.
Which statement best explains these observations?