1. Chemical Reactions
Chapter 7

2. The Nature of Chemical Reactions
Section 1

3. Chemical Reactions
Chemical Reaction: when a substance undergoes chemical changes, forming a new substance
Cannot be reversed
The new substance will have DIFFERENT chemical and physical properties than the original

4. Chemical Reactions
Some observations that suggest a chemical change has taken place…
Heat, light or sound
Production of a gas
Formation of a precipitate (“stuff forming”)
Change in color - This is not conclusive proof though, it needs to be proven that some new compound is present.

5. Chemical Reactions Reactants: Starting materials in a reaction
Products: Ending materials in a reaction
The products of a reaction are made up of the same number and type of atoms as the reactants, they have just been rearranged

6. Chemical Reactions
C6H12O6 + 6O2  6CO2 + 6H2O Glucose and oxygen react to form carbon dioxide and water
Same number and kind of atoms on each side, just in different arrangements, it has changed into a different molecule.

7. Chemical Reactions
Chemical reactions involve breaking old bonds followed by the making of new ones
Breaking bonds RELEASES energy
Forming bonds REQUIRES energy
Energy stored in bonds = chemical energy
Activation Energy: The energy required to break enough bonds for a reaction to start

8. Exothermic Reactions Reactions that RELEASE energy
More energy in the reactants than the products
The extra chemical energy from the reactants is released as heat when the bonds in the products reform

9. Endothermic Reactions
Reactions that ABSORB energy
More energy needed to break the bonds than is released

10. Chemical Equations
section 2

11. Remember!
All MATTER and ENERGY are conserved, but they can change forms
What goes in must come out, but it can be rearranged!
You have to account for all the stuff that goes into the reaction

12. Chemical Equations
Chemical reactions are shown with chemical equations
Reactants  Products
A chemical equation uses symbols to show the relationship between the reactants and products

14. Balancing Equations
An equation is balanced when the number of molecules/atoms in the reactants matches those in the products
An equation is balanced by changing the ratios of molecules/atoms so each side has the lowest possible same whole number and type of atoms

15. Balancing Equations
A coefficient is a number that shows the relative amount of a compound in a reaction
You CAN change the coefficient in front of any atom/molecule
You CANNOT change the subscript (this would change the formula of the molecules)

16. C6
H12 O6 +
6O2 6C +  O2
6H2 O
Carbon - 6
Carbon - 6
Hydrogen - 12
Hydrogen - 12
Oxygen - 18
Oxygen - 18

17. Let’s Practice!
_____H2 + _____ O2  ____ H2O

18. Let’s Practice!
____ H2 + ____ N2  ____ NH3