# Kinetics Class #2 OB: mastering the art of the potential energy diagram, and a few vocabulary words to go with them.

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Kinetics Class #2 OB: mastering the art of the potential energy diagram, and a few vocabulary words to go with them

Chemical reactions occur when enough particles collide with sufficient energy (but not too much) and these collisions occur with proper orientation of the particles. Any process that encourages more and stronger collisions will decrease the time it takes for a chemical reaction to happen, or more importantly, they will increase the rate of the chemical reaction. The rate of a Chemical Reaction = 1 time

Let’s draw the potential energy diagram for sodium hydroxide dissolving into water Time of the reaction… Potential energy kJ/mole

sodium hydroxide dissolving into water Time of the reaction… Potential energy kJ/mole First, write yourself the balanced thermochemical equation, and make note of exo or endothermic… NaOH (S) Na +1 (AQ) + OH -1 (AQ) + energy ΔH = -44.51 kJ (exo)

sodium hydroxide dissolving into water Time of the reaction… Potential energy kJ/mole Now we draw NaOH (S) Na +1 (AQ) + OH -1 (AQ) + energy ΔH = -44.51 kJ (exo)

sodium hydroxide dissolving into water Time of the reaction… Potential energy kJ/mole Now we draw NaOH (S) Na +1 (AQ) + OH -1 (AQ) + energy ΔH = -44.51 kJ (exo) -ΔH-ΔH AE reactants products We don’t know the actual levels, but we know that this difference is 44.51 kJ/mole Represents the activation complex, the transition between R + P.

Vocab x 5 Potential energy – the energy stored in the bonds of the reactants or the products Activation energy – the energy it takes to start a chemical reaction. It must be sufficient or else. Activation complex – the transitional state of being, where reactants are coming apart but are not yet products ΔH – the difference between the potential energy of the reactants and the potential energy of the products Potential energy diagram – a graph showing the flow of energy of a chemical reaction. Can be exo or endothermic

Draw the potential energy diagram for the synthesis of aluminum oxide. Label the reactants, products, AE, AC, ΔH (make it + or – as needed), and put labels on the graph, and a title too. Go!

PE diagram for synthesis of aluminum oxide ΔH = -3351 kJ/mole Al + O 2 Al 2 O 3 -ΔH-ΔH AE AC PE kJ/mole Time of the reaction

In an endothermic reaction, energy is absorbed, the products have more energy in them than the reactants had. Where does this energy come from? (the environment – which is why these reactions feel cold. They “steal” energy from the immediate surroundings, bringing into the bonds of the reaction. We will attempt to draw the PE diagram for the dissolving of sodium chloride into water NaCl Na +1 + Cl -1 + energy ΔH = +3.88 kJ/mole Go!

Table salt dissolves in water, ΔH = +3.88 kJ/mole PE kJ/mole Time of reaction

Table salt dissolves in water, ΔH = +3.88 kJ/mole PE kJ/mole Time of reaction

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Table salt dissolves in water, ΔH = +3.88 kJ/mole PE kJ/mole Time of reaction salt Ions in solution +ΔH+ΔH AE

Draw the PE diagram for the combustion of propane. Indicate the PE of reactants, products, AE, AC, ΔH, and a title. title Y axis label X axis label

Draw the PE diagram for the combustion of propane. Indicate the PE of reactants, products, AE, AC, ΔH, and a title. The combustion of propane ΔH = -2219.2 kJ/mole P E kJ/mole Reaction time C 3 H 8 + O 2 CO 2 + H 2 O -ΔH-ΔH AE NOTE: the PE of the products is less than the PE of the reactants. Where is the missing energy? Matter, nor energy, can be created or destroyed in any chemical reaction, or physical change.

Let’s look over the celebration for solutions and water now. Homework tonight… Kinetics HW #2

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