Chemical Reactions Notes

Chemical Reaction Definition:  When substances combine to form a new substances.

Chemical Equations…  Uses symbols to show reactants + products of a chemical reaction.  REACTANTS: materials that you start with (left side)  PRODUCTS: materials that you end with (right side)  EXAMPLE: 2 H 2 + O 2  2 H 2 O reactants products  Uses symbols to show reactants + products of a chemical reaction.  REACTANTS: materials that you start with (left side)  PRODUCTS: materials that you end with (right side)  EXAMPLE: 2 H 2 + O 2  2 H 2 O reactants products

1. Practice Questions:  4 Al + 3 O 2  2 Al 2 O 3 ProductsReactants

2. Practice Questions:  CO + 2H 2  CH 3 OH ProductsReactants

3. Practice Questions:  AgNO 3 + NaCl  AgCl + NaNO 3 ProductsReactants

4. Practice Questions:  3Fe + 2O 2 Fe 3 O 4  3Fe + 2O 2  Fe 3 O 4 Products Reactants

C. Law of Conservation of Mass  mass of products = mass of reactants  What goes in…must come out!  mass of products = mass of reactants  What goes in…must come out!

Example: 2 H 2 + O 2  2 H 2 O reactants products Elements: H + O

Practice Questions  1. What elements would be the reactants?  products: Sn + 2H 2 O  1. What elements would be the reactants?  products: Sn + 2H 2 O Sn, H, O

Practice Questions  2. What elements would be the reactants?  products: 2 Al 2 O 3  2. What elements would be the reactants?  products: 2 Al 2 O 3 Al, O

Practice Questions  3. What elements would be the products?  reactants: 2 Fe + 2 H 2 SO 4  3. What elements would be the products?  reactants: 2 Fe + 2 H 2 SO 4 Fe, H, S, O

Counting the molecules and compounds:  Coefficient: the number in front of the chemical formula - it tells how many molecules of a substance. 2 Fe

Example:  2 H 2 O atoms of “H” per molecule atoms of “O” per molecule atoms of “H” total atoms of “O” total  2 H 2 O atoms of “H” per molecule atoms of “O” per molecule atoms of “H” total atoms of “O” total The coefficient times subscript = the number of atoms total!!!

This equation is balanced because the number of H’s and O’s on product and reactant sides are equal.  2 H 2 + O 2 -> 2H 2 O H O H O  2 H 2 + O 2 -> 2H 2 O H O H O

1. CH 4 + O 2  CO 2 + H 2 O  C – 1 H – 4 O – 2 C– 1 O – 3 H – 2  Not balanced  C – 1 H – 4 O – 2 C– 1 O – 3 H – 2  Not balanced

2 Na + I 2  2 NaI 2. 2 Na + I 2  2 NaI  Na I Na I  balanced  Na I Na I  balanced

N 2 + O 2  N 2 O 3. N 2 + O 2  N 2 O  N O N O  Not balanced  N O N O  Not balanced

2KI + Cl 2  KCl + I KI + Cl 2  KCl + I 2  K I Cl K I Cl  Not balanced  K I Cl K I Cl  Not balanced

S + O 2  SO 3 5. S + O 2  SO 3  S O S O  Not balanced  S O S O  Not balanced

Controlling Chemical Reactions  Most chemical reactions involve a transfer of energy.  Some reactions release energy.  Some reactions absorb energy.  Release energy: exothermic reaction  Absorb energy: endothermic reaction  Most chemical reactions involve a transfer of energy.  Some reactions release energy.  Some reactions absorb energy.  Release energy: exothermic reaction  Absorb energy: endothermic reaction Melting ice cube Burning candle Ex othermic = energy ex its En dothermic = energy in

Activation Energy…  Energy needed to start or begin a reaction  Enzymes and Catalysts can change the rate of a reaction…(ex. Enzyme in your saliva)  Match used to start a fire.  Energy needed to start or begin a reaction  Enzymes and Catalysts can change the rate of a reaction…(ex. Enzyme in your saliva)  Match used to start a fire.