Chemical Reactions

How is a chemical change different from a physical change?

• there is no difference

• a physical change creates a new substance

• a chemical change creates a new substance

What is true of a chemical reaction?

• the atoms stay together

• the atoms unbond, rearrange and then rebond to form the products

• new atoms are formed

• some atoms disappear

What happens in an endothermic reaction?

• the temperature decreases

• the temperature increases

What happens in an exothermic reaction?

• the temperature decreases

• the temperature increases

In a chemical reaction, mass is conserved. What does that mean?

• that type and number of atoms and the mass stay the same

• the mass of the reactants stays the same

• the mass of the products stays the same

• the mass of the products is always twice that of the reactants

CH₄ + 2O₂ ---> CO₂ + 2 H₂O

Count the atoms in the reactants

• C= 4 H=4 O=1

• C= 1 H=4 O=4

• C=1 H=4 O=1

CH₄ + 2O₂ ---> CO₂ + 2 H₂O

Count the atoms in the products

• C=1 H=4 O=1

• C=4 H=1 O=1

• C=1 H=4 O=4

In the following equation, what are the REACTANTS?

2C₃H₆+ 9O₂ ---> 6CO₂ + 6H₂O

propane +oxygen ---> carbon dioxide and water

• propane and oxygen

• carbon dioxide and water

In the following equation, what are the PRODUCTS?

2C₃H₆+ 9O₂ ---> 6CO₂ + 6H₂O

propane +oxygen ---> carbon dioxide and water

• propane and oxygen

• carbon dioxide and water

What is the purpose of a catalyst in a chemical reaction?

• speed up the reaction

• slow down the reaction