Energy in Chemical Reactions

What is Energy? The ability to do work or produce heat. Potential Energy – stored energy. Kinetic Energy – energy of motion.

What is Enthalpy? The quantity that measures changes in energy in systems. (energy released or absorbed) Enthalpy change is always the difference between the enthalpies of the products and the reactants.

System – the participating members of a reaction or change. Surroundings – everything outside the system. Where energy changes are measured

Heat: the total amount of energy transferred Heat: the total amount of energy transferred. Heat transfers from hot to cold. Cold is the absence of heat, or energy. Temperature: average kinetic energy (random motion) of all the particles in a system. The faster they move, the hotter they are.

Endothermic – heat energy absorbed Exothermic – heat energy given off

Energy! Chemical Reactions are occurring everywhere. From the ignition of your car, to the burning of fuel, and the rusting of the gas tank, interacting particles will always… combine, break apart, and reorganize in order to achieve lower energy & stability

Reaction Diagram Products Potential Energy Reactants Reaction

Activation Energy (a) - the minimum energy necessary to start a chemical reaction. This energy comes from the surroundings a Potential Energy Reaction

∆H is the Change in Enthalpy ∆H = Energy of Products – Energy of Reactants Potential Energy ∆H Reaction

Within the “system” Exothermic Reactions: energy is given off from the reaction. This will result in a negative enthalpy (-ΔH). E N R G Y a -ΔH Reaction

Within the “system” Endothermic Reactions: energy is absorbed from the reaction. This will result in a positive enthalpy (+ΔH). E N R G Y a +ΔH Reaction

Catalyst A catalyst is a substance which increases the rate of a reaction without being consumed itself. Effect of a Catalyst: a catalyst will lower the activation energy of a reaction. This will speed up the rate of the reaction.

Assignment Reaction Rate Inquiry – due today Energy WS #1: Reaction Rates Packet – due next class

Wrap up 1. What does endothermic mean? 2. What does exothermic mean?

Wrap up Label the parts of the reaction diagram: a,b, & c. Is it endo or exo?

Drill – 6/7/10 Give an example of an endothermic reaction and an exothermic reaction

Drill #67 – 5/22/12 Compare/contrast the following terms: exothermic and endothermic potential and kinetic energy