Modeling Chemical Reactions - 2

Modeling Chemical Reactions - 2

Open Ended

Early in the day, Will learned about the kinds of changes in matter that can take place.He wanted to explore these changes in more depth, so he compared the two kinds of ways matter changes and how they differ. He recorded his findings in his science notebook. What are the ways in which matter changes and how do they differ?

Sample

The two kinds of changes in matter are physical changes and chemical changes. When physical changes occur, the material may change shape or appearance, but its composition remains the same. Boiling, freezing, cutting, bending, or crushing change a material’s appearance, but the chemical bonds are not affected. Chemical changes occur when chemical bonds rearrange to form new substances. Burning and rusting are examples of chemical change.

Multiple Select

After having studied chemical reactions in school, Jose knew that when oxygen and hydrogen gases combine in the correct amounts, the combination yields a new substance, water. Choose the correct statements.

• hydrogen and oxygen are reactants

• hydrogen and oxygen are products

• water is a reactant

• water is the product

​Explanation

​Reactants are substances that undergo chemical change, and products are the result of change. Since the hydrogen and oxygen are undergoing the change, they are the reactants. When they react, they produce water.

Multiple Choice

After learning about the law of conservation of mass, Remy began to wonder about how to best test this law. She wanted to show that the total amount of matter did not change, but a process produced the same amount of different kinds of matter. What is the best way to study this law?

• in a homogeneous mixture

• in a heterogeneous mixture

• in an open system

• in a closed system

Open Ended

Diego is performing an experiment using the equipment shown in the diagram. He places filings of zinc metal into a clear colorless mixture of hydrochloric acid and water and then seals the flask with a stopper as shown. He observes that the liquid in the flask bubbles and becomes hot. As time progresses, the zinc metal disappears, and the water level in the cylinder moves down as it fills with gas. Eventually, the bubbles stop forming and the flask contains a colorless liquid, while the cylinder is nearly empty of water. Diego argues that what is happening is just a physical change of the water in the flask boiling to produce water vapor, which is filling the cylinder. A classmate disagrees and hypothesizes that a chemical reaction has occurred. Provide evidence for the classmate’s hypothesis.

​Sample

​The process is a chemical reaction because there was a gas produced without the addition of heat, which is necessary for boiling, and the gas in the cylinder did not condense. The heat came from the mixture itself and was not added to the system.

Poll

How do you feel about modeling chemical reactions?

• What is a chemical reaction?

• Oh yeah, I think I have heard of those.

• Feeling pretty confident.

• Bring on the quiz!

​Explanation

​A closed system retains both products and reactants. A and B do not involve chemical reactions, so A and B are not correct. Products may be lost from an open system, so C is not correct.