Chapter 9 - Chemical Reactions and Equations

What happens in a chemical reaction?

• bonds between atoms break and/or are formed

• new atoms are created and/or removed

• protons move from one atom to another

• electrons change into protons

How are chemical bonds formed?

• atoms duplicate themselves

• electrons move from one atom to another

• the number of protons and electrons in an element is changed

• through changes in an atom's nucleus

Which of the following would indicate that a chemical reaction has occurred?

• a new element has been created

• a different substance has formed

• the total mass has either increased OR decreased

• the total number of elements has either increased OR decreased

This is a model of a molecule. What would this molecule look like in a chemical formula?

• CH

• C4H

• CH₄

• 4CH

Which would indicate a chemical equation is balanced?

• if the number of atoms in the reactants is the same as the number of atoms in the products

• if the atoms have ionic OR covalent bonds

• if the atoms have full valence shells

• if the total energy has remained the same

BEFORE the equation is balanced, how many hydrogen atoms are present on the reactant side?

_____ C₄H₆O₃ + _____ H₂O --> _____ C₂H₄O₂

• 6

• 2

• 12

• 8

Why does the number of carbon atoms need to be the same on both sides of the reaction?

_____ C₄H₆O₃ + _____ H₂O --> _____ C₂H₄O₂

• in a chemical reaction, no new atoms can be made

• because the number of oxygen atoms must be balanced with the number of carbon and hydrogen atoms

• because the coefficients and the subscripts need to be equal

• it does NOT need to be the same

What coefficient should go in the last blank space in order for the equation to be balanced?

_____ C₄H₆O₃ + _____ H₂O --> _____ C₂H₄O₂

• 1

• 2

• 3

• 4

How many hydrogen atoms are present in 3H₂O?

• 6

• 3

• 2

• 1

In the molecule below, which of the following choices is a subscript?

3H₂O

• 3

• 2

• H

• O