2.4

Write one sentence that uses the words "chemical reaction," "reactant," and "product."

A chemical reaction changes reactants into products.

Label the reactants and products in the chemical reaction: CH4+2O2----------------------> CO2+2H2O. Write brief definitions for these terms next to their labels.

CH4+2O2- reactants: the substances changed during a chemical reaction; they are located on the left side of the equation CO2+2H2O- products: the substances made by a chemical reaction; they are located on the right side of the equation

The prefix exo- means "out," and the prefix endo- means "in." What do these prefixes tell you about exothermic and endothermic reactions?

Energy goes out of an exothermic reaction and goes into an endothermic reaction.

Write your own analogy to remember the meaning of activation energy.

The energy it takes to get out of bed in the morning before you can start your day.

The term "equilibrium" is based on two Latin roots that mean "equal" and "balance." How do these meanings tell you the meaning of equilibrium in a chemical reaction?

The reactants and products are formed equally; the reaction is in a balanced state.

Before a chemical reaction can start, _____________ must be absorbed by the reactants. The amount that must be absorbed to start the reaction is called the _____________.

energy; activation energy

the amount of energy that needs to be absorbed for a chemical reaction to start

activation energy

The _____________ of the reactants and products determines whether energy will be released or absorbed during a chemical reaction.

bond energy

changes substances into different substances by breaking and forming chemical bonds

chemical reaction

a chemical reaction that absorbs more energy than it releases

endothermic reaction

is reached when both the reactants and products are made at the same rate

equilibrium

a chemical reaction that releases more energy than it absorbs

exothermic reaction

In an endothermic reaction, the products have a _____________ bond energy than the reactants. Overall, energy is _____________.

higher; absorbed

In an exothermic reaction, the products have a _____________ bond energy than the reactants. Overall, energy is _____________.

lower, released

In a chemical equation, what symbol is used to show that a chemical reaction goes in both directions?

one arrow on top of another, pointing in opposite directions.

the substance made by a chemical reaction

product

the substance that is changed during a chemical reaction

reactant

What causes chemical bonds to break during a reaction?

the addition of energy to the reactants.

What is bond energy?

the energy required to break a bond between two atoms.

When does a chemical reaction reach equilibrium?

when a reaction takes place at equal rates in both directions.