Modeling Chemical Reactions - 1

Modeling Chemical Reactions

Multiple Select

Leann is learning about chemical reactions. She wants to create a model of a chemical reaction, so she is examining the information that she should include. What are the different components that she should include in her model? Choose the three that apply.

• the kinds of atoms that form during a reaction

• the kinds of molecules involved in the reaction

• the kinds of elements that make up a molecule

• whether the molecules are products or reactants

• whether the products have more mass than the reactants

​Explanation

​A chemical equation shows the reactants and products, the kinds of molecules involved in the reaction, and the kinds of elements that make up a molecule. Due to the law of conservation of mass, new products always have the same amount of matter as the reactants. Atoms are not formed but are already present and combine to form the molecules shown in the equation.

Multiple Choice

One day on her walk home from school, Leann noticed some rust on an old car. Leann knows that when iron and oxygen chemically react, they can form rust. She remembered that models can be used to summarize what happens in a chemical reaction. She decides to create a model of this chemical reaction. What is the name that describes the iron and oxygen found on the left side of Leann's model?  

4 Fe + 3O₂ → 2Fe₂O₃

• products

• reactants

• scientific notation

• synthesis

​Explanation

​The correct answer is “reactants.” These are the parts that react together in a chemical reaction to form a new product. Synthesis is incorrect because it describes the type of chemical reaction. Scientific notation is a way of writing a chemical reaction but is not the name of the parts on the left side.

Multiple Choice

Keesha performed a chemical reaction, and the products looked quite different from the reactants. She knew the amount of matter had not changed due to the law of conservation of mass. According to the law of conservation of mass, what happens in a chemical reaction?

• Matter is not created or destroyed and the same amount of mass remains.

• A new kind of matter is created and the amount of mass either increases or decreases.

• Matter is not created or destroyed and the amount of mass may change after the reaction.

• New matter is created and changes form so that the mass of the reactants and the products will almost be equal.

​Explanation

​The correct answer is “Matter is not created or destroyed, and while the products may appear different, the same amount of mass remains.” All other answers indicate that there is a change in the amount of mass during a chemical reaction, which is not correct.

Multiple Select

Hydrogen peroxide (H₂O₂) is a liquid people mix with water and use to disinfect skin wounds. Under certain conditions, the hydrogen peroxide molecule (H₂O₂) will break down and form water (H₂O) and oxygen (O₂). Look at the diagram showing before and after the molecule breaks down. What evidence supports that mass is conserved during this chemical reaction? Choose two that apply.

• Hydrogen and oxygen atoms are involved.

• The number of atoms is the same on both sides of the equation.

• The types of atoms to the right of the arrow are the same as those to the left of the arrow, but have been rearranged.

• There are the same number of oxygen atoms as hydrogen atoms.

​Explanation

​The correct answers are B and C. As the equation shows, the types of atoms and the number of atoms remain the same before and after the chemical reaction. There are four atoms of hydrogen (H) and four atoms of oxygen (O) on both sides of the arrow. The only change is the arrangement of the atoms, so the mass remains the same. This supports that mass is conserved during a chemical reaction. The statement that hydrogen and oxygen atoms are involved in the reaction is true, but does not describe what happens to the atoms during the reaction, so A is not correct. The statement that there are the same number of oxygen and hydrogen atoms is also true, but does not tell what happens to the number of atoms after the reaction (that it stays the same), so D is not correct.