Exothermic
?H = - Energy Released
Product has less potential energy that reactions. There is a net loss of energy because energy is released to make the product.
Endothermic
?H = + Energy Absorbed
Product has more potential energy that the reactants. There is a net gain of energy because more energy was absorbed to form the activated complex than was released to form the product.
Kinetic Energy
Energy of motion; how fast particles are moving
Potential Energy
Energy of position or composition; the ability to do work or produce heat; stored in chemical bonds
Potential Energy Diagram
A diagram of reaction progress that shows the potential energy change that occur during a chemical reaction. Potential energy is on the y-axis and the reaction progress on the x-axis.
Activated complex
the temporary, intermediate product in a chemical reaction that may break apart and re-form the reactants or may form new products.
The top of the curve on a potential energy diagram
Activation energy
Amount of energy needed to form the activated complex from the reactants. The minimum amount of energy required to start a chemical reaction.
Equilibrium
(chemistry) A state of balance in which a chemical reaction and the reverse chemical reaction occur at the same rate. It can only occur in a closed system.
(quantities of reactants and products not equal)
Stress
(chemistry) Any change in temperature, concentration or pressure on an equilibrium system
Le Chatelier's Principle
When a stress (such as a change in concentration, pressure, or temperature) is applied to an equilibrium, the reaction will shift in a way that relieves the stress and restores equilibrium
Catalyst
(chemistry) A substance that initiates or accelerates a chemical reaction without itself being affected or changed.
Effect of Catalyst
Changes the rates of both the forward and reverse reactions equally. It may cause equilibrium to be established more quickly but does not change any of the equilibrium concentrations
Entropy
A measure of the randomness or disorder of a system. The greater the disorder, the higher the level of entropy.
Kinetics
branch of chemistry that is concerned with the rates of chemical reactions
Collision Theory
In or for a reaction to occur, reactant particles must collide
Factors Affecting Rate of Reaction
1. Nature of the reactants - ionic reacts faster than covalent
2. concentration
3. surface area
4. Catalyst
5. Temperature
6. Pressure (gases only)
Chemical Reaction
breaking of existing bonds and the formation of new ones
Nature of Reactants (Rate of Reaction)o
Chemical bonds contain potential chemical energy.
Covalent Bonds - slower to react because more bonds must be broken before reaction can occur.
Ionic Substances - have fewer bonds so reactions occur more quickly.
Concentration (Rate of Reaction)
Increase concentration of reactants increases rate of reaction (faster)
Surface Area (Rate of Reaction)
The bigger the surface area the faster the reaction rate
Pressure (Rate of Reaction)
No effect on reaction rates of Solid or liquid.
Gas - increase pressure increases the concentration of gaseous particles so the rate of reaction is increase if the reaction involves only gases.
Presence of Catalyst (Rate of Reaction)
increases rate of reaction by providing a different and easier pathway for a reaction, it reduces the activation energy.
Temperature (Rate of Reaction)
The greater the temperature of a substance the faster the molecules move which means there wiil be more collisions increasing the rate of reaction.
Collision of Molecules
molecules must be arranged in a specific way when they collide in order for a reaction to occur.
Heat of Reaction (?H)
?H (heat of reaction) = Difference between the potential energy of reactants and the products
Physical Equilibrium
Equilibrium between two phases of same substance; Example: H2O(L) <-> H2O (g) water changing from liquid to gas and then back to a liquid in closed system.
Rate of evaporation is equal to the rate of condensation.
Solution Equilibrium
Solids in liquids exist in equilibrium in a saturated solution
Chemical Equilibrium
in a reversible chemical reaction, the point at which the rate of the forward reaction equals the rate of the reverse reaction. (must be a closed system)
Entropy Solid to Liquid to Gas
From highly organized to highly random arrangement of particles.
Solid(great order, low entropy) To
Liquid (more random, higher entropy)
Gas (maximum randomness, highest entropy)
Exothermic Phase Changes
Freezing (L->S), condensing (G->L), deposition (G->S)
Potential Energy Diagram
Shows the energy of reactants and products throughout the progress of a chemical reaction
Enthalpy (?H)
the amount of thermal energy emitted or absorbed by a chemical reaction, under conditions of constant pressure