Physical Science

Outline of Chemical Reactions

1. Law of Conservation of Mass

• Total mass of reactants = total mass of products.

2. Chemical Equations

• Description of reactions using element symbols and chemical formulas.

• Reactants: Starting substances (left of the arrow).

• Products: Substances produced (right of the arrow).

• Separation of reactants/products by plus signs.

3. Bond Formation and Breaking

• Atoms rearrange when chemical bonds break.

• Energy required for particles to collide and break bonds.

• No new atoms created; existing atoms rearrange.

4. Changes in Matter

A. Physical Changes

• Do not produce new substances; properties may change.

B. Chemical Changes

• Produce new substances; different properties than reactants.

• Examples: Change in color, odor, bubble formation, precipitate.

• Energy changes: Warming, cooling, light release.

5. Types of Chemical Reactions

A. Synthesis Reaction

• Two or more substances combine: A + B → C.

B. Decomposition Reaction

• One compound breaks down: AB → A + B.

C. Replacement Reaction

• Single Replacement: One element replaces another in a compound.

• Double Replacement: Negative ions switch places in two compounds.

D. Combustion Reaction

• Substance combines with oxygen, releasing energy (thermal and light).

6. Reaction Rate Factors

A. Surface Area

• Increased surface area increases collision rate.

B. Temperature

• Higher temperatures increase particle speed, leading to more collisions.

C. Concentration and Pressure

• Higher concentration increases collision rates; increased pressure in gases brings particles closer together.

7. Energy Changes in Reactions

A. Activation Energy

• Minimum energy required to initiate a reaction.

B. Exothermic Reactions

• Release thermal energy; more energy released when a bond is broken in the products.

C. Endothermic Reactions

• Absorb thermal energy; require constant energy input to continue. More energy is required to break bonds in the reactants

Key terms: endothermic and exothermic

• exothermic need to release more energy to form a bond in the products than to break a bond in the reactants

• endothermic need more energy to to break the bonds in the reactants than to create bonds in the products