Chemical Reactions

I. Chemistry• A. We already know that in order to create compounds

we need to take different elements and bond them together. What are the different types of bonds? What part of the atom is involved?

• B. Chemical reactions is a change in which one or more substances are converted into new substances.

Baking a cake, hydrolysis, photosynthesis1. Nuclear reactions – when the nucleus is involved with the energy transfer…fission or fusion

II. Chemical Reactions

• A. Chemical reactions: transform one set of chemicals into another by changing bonds between atoms– 1. Can occur quickly or slowly

• B. Chemical reactions have two parts:– 1. Reactants: elements or compounds that enter the

reaction (what you start with)– 2. Products: elements or compounds that are produced

(what you end up with)

II. Chemical Reactions

• Examples2H₂ + O₂ 2H₂O_______ _______

C₆H₁₂O₆ + 6O₂ 6CO₂ + 6H₂O + ATP __________ __________

III. Conservation of Mass

• A. Total mass of products in a chemical reaction will always equal the mass of the reactants.

• B. Antoine Lavoiser “father of modern chemistry” explained the law of conservation of mass and chemical reactions through nomenclature & stoichiometry

IV. Writing Equations

• A. Chemical equations a way to describe a chemical reaction using chemical formulas and other symbols.

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IV. Writing Equations

• B. Remember the law of conservation of mass:– 1. Balancing equationCoefficient: 4 H2O subscript: CO2

How many hydrogen atoms How many C & O?

Oxygen?

8 hydrogen atoms 1 carbon atom4 oxygen atoms 2 oxygen atoms

Practice

____CO + ____O2 ____CO2

___KNO3 ____KNO2 + _____O2

____O3 _____-O2

V. Energy in Reactions • A. Whenever chemical bonds form or are broken

energy is released or absorbed. (bioenergetics)– Think about after you ingest a meal

• B. Energy change is a good indicator if a chemical reaction will occur.

• C. Chemical reactions that release energy often occur spontaneously

• D. Chemical reactions that absorb energy will not occur without a source of energy

V. Energy in Reactions

• Examples– Reactions that release energy

Pure Sodium + Water

– Reactions the absorb energy(Take the energy of stirring)

Cold Packs

V. Energy in Reactions• E. Types of reactions:– 1. Exergonic – products

have less energy than the reactants. Energy is given off.

– Example: food being oxidized in mitochondria of cells.

– 2. Endergonic – products have more energy than the reactants. Energy is required.

– Example: plants using CO2 and water to form sugars.

VI. Activation Energy• A. The energy needed for a chemical reaction to

start is known as activation energy.– 1. Every cell needs a little bit of energy to begin breaking

down molecules.

• B. Examples

VII. Enzymes• A. Some chemical reactions that make life possible

are to slow or have very high activation energies therefore our cells compensate by making catalysts

• B. Catalysts are substances that speed up reactions by lowering the activation energy without altering reaction.

• C. Enzymes are proteins that act as catalyst inside a cell.