Chemical Reactions Ch.21 Sec.1

Chemical Reactions • Occurs with chemical changes • Make new substances • Change in which one or more substances are converted into new substances

Signs of Chemical Reactions • Change in color • Release of light, heat, gas, sound, or smell

Examples of Chemical Reactions • Growing • Ripening • Decaying • Burning • Rusting

Law of Conservation of Mass • Mass cannot be created or destroyed • Chemical reactions rearrange atoms • Break bonds, rearrange, and make new bonds • Energy breaks bonds

Chemical Equation • A way to describe a chemical reaction using chemical formulas and other symbols • Pg. 635; Table 1 and equation

Products & Reactants • Reactants = left side of equation (ALWAYS) • Products = right side of equation (ALWAYS)

Chemical Equations • Balanced chemical equation – has same number of atoms of each element on both sides of the equation • Satisfies the Law of Conservation of mass.

Reaction Types 1. Synthesis 2. Decomposition 3. Single Displacement 4. Double Displacement 5. Combustion

Synthesis  Combines 2 substances to make 1 compound  A + B --> AB  Blue + Red --> Purple  Na + Cl --> NaCl  1 Product

Synthesis

Decomposition  Takes 1 compound and breaks it apart into 2 or more substances  AB --> A + B  H 2 O --> H 2 + O 2  Opposite of synthesis  1 Reactant

Decomposition

Single-Displacement  1 element swaps places with another element that is in a compound  XA + B --> XB + A  B and A swapped places  ** Has 1 compound and 1 element on both sides  Ex: CuCl 2 + Al --> AlCl 3 + Cu

Single-Displacement

Double Displacement  2 compounds exchange elements with each other  AX + BY --> AY + BX  ** 2 Compounds on both sides  Ex: NaCl + AgF  NaF + AgCl

Double Displacement

Combustion  Oxygen and another compound BURN to make new products  Oxygen is ALWAYS a reactant  CO 2 + H 2 O is ALWAYS a product  Ex: CH 4 + O 2 --> CO 2 + H 2 O

What Type of Reaction?  Double Displacement  Decomposition  Single Displacement  Synthesis 1. HCl + NaOH --> H 2 O + NaCl 2. NaCl --> Na + Cl 2 3. Al + Fe 2 O 3 Al 2 O 3 + Fe --> 4. P 4 + O 2 --> P 4 O 10

2 Types Energy Reactions 1. Endothermic 2. Exothermic

Endothermic • Endo = in • Energy is taken in (absorbed) with reactants • Drops surrounding environment temp.

• Ex: Photosynthesis takes in sunlight

Exothermic • Exo = out • Energy is released or given out with products • Raises surrounding environment ’ s temperature • Ex: hand warmers

1. Exo 2. Exo 3. Endo 4. Exo Exo or Endo?

1. Paper burning 2. Firecracker Exploding 3. Plant making its own food 4. Electric blanket

Reaction Rate • • How fast a reaction is going Factors on rate: 1. Temperature 2. Surface Area 3. Concentration 4. Stirring 5. Catalysts

Catalysts • Substance that speeds up reaction without being permanently changed • Ex: Enzymes in our stomach speed up digestion (lactose)

Inhibitors • Substance used to slow down a chemical reaction • Ex: Food preservatives (prevent spoilage) • Product is not changed just how fast or slow the rate of production occurs