Chemical Reactions: Chapter 7 Workbook pages Due tomorrow Taking Notes today

Chemical Reactions and the Five Basic Reaction Types

Chemical Reaction What is a chemical reaction? A chemical reaction: is a process in which one set of substances called reactants is converted to a new set of substances called products. reactants  products

How do we know a chemical reaction has occurred ? Look for physical evidence to that shows a reaction has occurred: 1.a color change 2.formation of a solid (precipitate) within a clear solution 3.evidence of a gas 4.evolution or absorption of heat

How do we represent the chemical reaction in a way that is convenient and easy to understand? A chemical equation is a symbolic way of representing a chemical reaction in terms of chemical formulas. In a chemical equation, formulas for the reactants (starting substances in a chemical reaction) are written on the left sides of the equation and formulas for products are written on the right. The two sides of equation are joined by an arrow (  ).

Five Basic Reaction Types

1. Synthesis A + B  AB Two reactants form one product. + 

2. Decomposition AB + heat  A + B One reactant forms two products.

3. Single Replacement A + XY  X + AY B + XY  Y + XB An element and a compound react to form a different element and compound. Metals replace metals or hydrogen Nonmetals replace nonmetals

4. Double Replacement AB + XY  AY + XB Two compounds react to form two different compounds. The cations and anions switch partners. A&X are cations; B&Y are anions.

5. Combustion of a hydrocarbon C x H y + O 2  CO 2 + H 2 O + energy A hydrocarbon is composed of carbon and hydrogen atoms. This reaction is always exothermic since energy is a product. +

Reaction Rates and Equilibrium

What is the rate of a chemical reaction? Reaction rate is the speed of the reaction. It is the amount of time required for a chemical reaction to come to completion. Different reactions take different times Burning Aging Ripening Rusting

Collision Theory Atoms, ions and molecules can react to form products when they collide provided that the particles are orientated correctly and have enough kinetic energy. Particles lacking necessary kinetic energy to react bounce apart when they collide. The minimum amount of energy that particles must have in order to react is called the activation energy.

Activated Complex The minimum amount of energy that particles must have in order to react is called the activation energy.

Factors that Affect Reaction Rates Temperature Raise temperature, faster reaction rate Lower temperature, slower reaction rate Higher temperatures make molecules move faster because they have more kinetic energy so reaction is more likely Particle Size/Surface Area The smaller the particle size the smaller the surface area. The larger the particle size the larger the surface area. An increase in surface area, increases the amount of reactant exposed, which increases the collision frequency.

Catalyst Catalyst is a substance that increases the rate of a reaction without being used up itself during the reaction. Catalysts are NOT used up during the reaction. They help reactions to proceed at a lower activation energy than is normally required. Enzymes catalyze reactions in our body An inhibitor interferes with the action of a catalyst.

Catalyst Catalyst is a substance that increases the rate of a reaction without being used up itself during the reaction. Catalysts are NOT used up during the reaction. They help reactions to proceed at a lower energy than is normally required. Enzymes catalyze reactions in our body An inhibitor interferes with the action of a catalyst. Activation Energy without enzyme Activation Energy with enzyme Energy released during reaction with enzyme Without enzyme TIME ENERGY

Concentration The number of reacting particles in a given volume also affects the rate at which reactions occur. Cramming more particles into a fixed volume increases the concentration of reactants, the collision frequency and therefore, reaction rate.

20 Energy Energy is measured in Joules or calories Every reaction has an energy change associated with it Exothermic reactions release energy, usually in the form of heat. Endothermic reactions absorb energy Energy is stored in bonds between atoms

Exothermic reactions release energy, usually in the form of heat.

Endothermic reactions absorb energy, usually in the form of heat.

Three types of equilibrium 1. Phase equilibrium 2. Solution equilibrium 3. Chemical equilibrium

Equilibrium Equilibrium is the point where the reverse reaction is going as fast as the forward reaction. Sooo…. The rate of the forward reaction is equal to the rate of the reverse reaction. The concentration of products and reactants stays the same, but the reactions are still running.