Basic Chemical Reactions

What is a Chemical Reaction? A Chemical reaction occurs when ever a chemical bond is formed, broken or rearranged. A chemical reaction will always create a new substance.

Energy and Chemical Reactions When a reaction occurs it’s either going to give off energy or take in energy. Exergonic reactions – release energy (usually breaking bonds) Endergonic reactions – take in energy (usually making bonds)

Chemical Equations A chemical equation contains the following: Reactants: The starting chemicals Products: The ending (resulting) chemicals Yield sign: The arrow that shows the change. Coefficients: Numbers in front of the molecule. Subscript: Number behind and at the bottom of the atom or molecule.

Balancing Chemical Equations should balance. The number of atoms in the reactants should match the number of atoms in the product. You can not create or destroy energy or matter. Is this equation balanced?

Moles When trying to count very small particles like atoms a counting unit was created called the mole. 1 mole = x particles It is the number of particles in exactly 12 grams of carbon. Amedeo Avegadro was the Italian scientist who came up with this unit, so it is also called Avegadro’s Number.

Balancing Equations and Moles When we balance a chemical equation we are looking at the ratio of reactants and products. When we balance a chemical equation we are looking at the ratio of reactants and products. This is called a Molar Ratio. Example: 2Mg + O 2 2MgO The molar ratio of magnesium to oxygen is 2:1 So for every 2 moles of magenesium that react 1 mole of Oxygen will also react.

Law of Definite Proportions A compound will always contain the same elements in the same proportions regardless of how the compound is made or how it is formed.

Types of chemical Reactions There are three main types of chemical reactions: Synthesis Reactions Decomposition reaction Exchange reactions

Synthesis Reactions Synthesis means to combine. So a synthesis reaction is one where we are forming bonds to make a new molecule. This is the reaction that takes amino acids and combines them to make a protein. Anabolic activities.

Decomposition Reactions A decomposition reaction is when a lager molecule are broken down into its parts. These are called Catabolic activities Example: Glycogen produced by the liver is broken down into the sugar Glucose.

Exchange Reactions In an exchange reaction parts of the reactant molecules change partners. Example: When Glucose takes a phosphate group from ADT making ATD and GlucoseP.

Oxidation-reduction reaction There is a very important reaction called an Oxidation- reduction reaction (redox reaction) Redox reactions are both a decomposition and exchange reaction.

Oxidation-reduction reaction In a redox reaction an electron is given off by one reactant and accepted by another. The reactant loosing the electron is said to have been oxidized. The reactant taking the electron is said to have been reduced.

Oxidation-reduction reaction When an ionic bond is formed it is a type of redox reaction. However, when Hydrogen molecules are separated from their original molecules they take their electrons with them. This is also considered a redox reaction.

Rate of Reactions For a reaction to occur Valence electrons must slam into each other with enough force to either break bonds or make bonds. There are factors that will influence how well these valence electrons collide. -TemperatureConcentration Particle Size Catlysts Catlysts

Reaction Rate and Temperature An increase in temperature increase the kinetic energy of the particles and there fore they hit each other with more force.

Reaction Rate and Concentration The higher the Concentration the more likely the two reactants are to successfully hit each other and therefore react faster.

Reaction Rate and Particle Size Generally smaller particles move faster than large ones and therefore tend to collide more frequently.

Reaction Rates and Catalysts Catalysts are chemicals called enzymes that sped up the rate of reactions with out having to increase our body temperature.