1. Chemical Reactions
Section 2.4

2. Chemical reactions
When chemical reactions happen bonds between atoms are formed or broken, substances change into different substances.
When this happens inside organisms, it is called metabolism.

3. Substances that undergo chemical reactions are called reactants
Substances that undergo chemical reactions are called reactants. Reactants are what you begin with.
Substances formed are called products. Products are what you end up with.

4. There is a certain amount of energy required to start a reaction
There is a certain amount of energy required to break a bond.

5. Some Reactions release more energy
Some reactions absorb more energy

6. Writing Chemical Equations
Atoms are never created nor destroyed in a reaction, so equations (formulas that represent atoms and molecules) must always be balanced.

7. Example C + O - CO2 reactants products Na + Cl2 -- NaCl
Coefficient is the number in front of an atom or molecule. It tells how many molecules there are. It can be used to balance.
The subscription tells how many atoms of an element.

8. What do you need to balance the equation?
___ H2 + ____ O2 - ___ H2O
1,1,1
1,2,1
2, 1,2
2,2,2

9. What do you need to balance the equation?
______Fe +_____Cl2-- _____ FeCl3
3,2,3
2,3,2
2,1,2
1,2,1

10. What do you need to balance the equation?
___Cu +___AgNO3 - ___ Cu(NO3)2 +___ Ag
1,2,1,2
2,1,2,1
3,2,1,2
2,3,2,1

11. What do you need to balance the equation?
____Zn +___HCl - ___ZnCl2 +___ H2