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Presentation on theme: "CHEMICAL KINETICS AND EQUILIBRIUM Conner Forsberg."— Presentation transcript:


2 Chemical Kinetics Kinetics is the study of the rates at which chemical reactions occur and the mechanisms by which they occur. Rates are in terms of reactant consumed or products produced per unit of time. Mechanisms are the changes that make up the whole reaction. Chemical equations generally only show the overall process, not the intermediate steps that occur within

3 Heat

4 Energy Diagrams Potential energy diagrams show the changes in potential energy that occur during a reaction. They can indicate activation energy and whether the reaction is exothermic or endothermic. If the end of the graph is higher than the beginning, then it is endothermic (energy was gained from the surroundings). If the end of the graph is lower than the beginning, then it is exothermic (energy was lost to the surroundings). The ∆H of the reaction is the difference between the start of the graph and the end of the graph. Activation energy- The minimum energy needed to initiate a reaction. On the graph, this is the amount that it needs to rise to the highest point (where the activated complex exists).

5 Collision Theory Collision theory says that a reaction between molecules will occur if: The molecules are oriented properly. The molecules have enough energy (temperature!). If a reaction occurs, then the collision was effective. The frequency of these determines the rate. Key factors: What the reactants are- How many bonds need to change? Concentration- In a solution, are the particles far apart or close together? Temperature- A.k.a average kinetic energy; do these molecules have enough energy? Surface area- How many molecules are or able to be near each other? Catalysts- These increase the rate without being altered themselves. They do not start reactions, they just speed them up with an alternate pathway.

6 Chemical Equilibrium Equilibrium is, in short, when the rates of forward and reverse reaction (in a reversible reaction) are equal. This does not mean, however, that concentrations are equal. Chemical equilibrium is dynamic. Changes in the system are still occurring, they just balance each other. Equilibrium can be reached from either direction. In equilibrium, you can have a high amount of reactants or you can have a high amount of products. Some equilibria can lie very strongly toward a certain side, but still be in equilibrium. This reinforces the idea that concentrations do not have to be equal. Phase change equilibrium- A phase change is occurring at equal rates in both directions. Gas-Liquid Equilibrium- A system where an gas is above a liquid and it is in equilibrium. These are affected by temperature and pressure. Solubility equilibrium- A saturated solution.

7 Le Chatelier’s Principle Le Chatelier’s explains ways equilibrium can shift. Concentration Increasing one thing means that the system will consume whatever was increased, meaning that whatever wasn’t increased will increase in concentration. Decreasing the concentration of one thing will mean that system shifts to produce more of whatever was decreased. This will cause the other sides to be consumed. Pressure (when gases are involved) Increasing the pressure will increase the concentration of the side with fewer moles of gas. Decreasing the pressure will increase the side with more moles of gas. Temperature Increasing the temperature in an endothermic reaction will shift it to the products. Catalysts Equilibrium is more quickly achieved, however there is no overall change once it occurs (the equilibrium is the same as if there was not a catalyst).

8 Spontaneity and Entropy Spontaneous process- One that occurs in nature with a given set of conditions. Reactions tend to want to go to a lower energy state. Exothermic reactions are more easily spontaneous. Entropy- randomness in a system Gas>Liquid>Solid Higher disorder=Higher entropy Higher entropy=Higher temperatures Systems usually increase entropy.

9 It just gets better in AP…


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