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 (∆H)? The quantity that measures changes in energy in systems. It has the same of units as energy (kilojoules, joules, calories)

System – the participating members of a reaction or change. Surroundings – everything outside the system. This is where we measure energy changes. Whether the surroundings gain or lose energy.

Endothermic – heat energy absorbed Exothermic – heat energy given off

What is a Calorimeter? An insulated device that measures heat changes in a chemical reaction.

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. What is Temperature?: average kinetic energy (random motion) of all the particles in a system. The faster they move, the hotter they are.

Specific Heat Capacity (c) or (cp) Measure how well a substance absorbs or loses heat. The amount of heat energy it takes to raise the temperature of 1 gram of a substance, 1˚C. UNITS: Units in (J/g˚C) or (cal/g˚C) Low specific heat capacity – temperature changes easily, ex: metals High specific heat capacity – temp. changes slowly, substance retains its heat energy and will absorb it slowly. Ex: water

Chemical Reactions are occurring everywhere 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 (Ea) - the minimum energy necessary to start a chemical reaction. This energy comes from the surroundings Ea 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 Ea -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 Ea +ΔH Reaction

What is a 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.

Reaction Diagram WS!

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