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Rates of Reactions

Rates of Reactions. Part II of Unit II. Reaction Rate. Is the speed at which a chemical reaction occurs Measured by the change in concentration of a reactant or product over time Rate of rxn = Δ [A] /∆t * square brackets indicate the concentration of reactant or product ‘A’

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Rates of Reactions

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  1. Rates of Reactions Part II of Unit II

  2. Reaction Rate • Is the speed at which a chemical reaction occurs • Measured by the change in concentration of a reactant or product over time • Rate of rxn = Δ[A] /∆t * square brackets indicate the concentration of reactant or product ‘A’ • Units of mol/s or mol/L·s which can also be written as: mol L-1s-1

  3. Factors that affect the Rate of Reaction • Nature of Reactants • Tendencies toward bond formation • Ability of an atom to gain or lose electrons • Surface Area - Ability of reactants to meet • Solid reactant with a gas reactant would be much slower than two gas reactants • Surface area of a solid is increased by decreasing the particle size

  4. http://www.youtube.com/watch?v=Jg7mLSG-Yws

  5. Temperature • Increasing the temperature generally increases the rate of reaction • Recall that kinetic molecular theory states that molecules move faster at higher temperatures, thus have more kinetic energy. This allows molecules greater ability to react.

  6. Catalyst • A catalyst is a substance that increases the rate of a reaction but is not consumed in the reaction. • Examples are: • platinum in catalytic converters, which convert carbon monoxide to carbon dioxide a lesser of two evils. • Enzymes, which are proteins that attach to a reactant(s) and allow for a chemical rxn to occur then unattach.

  7. Concentration • Generally increasing the concentration of reactants will speed up a rxn • As a rxn proceeds, the concentration of reactants decreases and consequently so does the rate • If you were to graph concentration of reactant vs. time it would be curved...

  8. Concentration vs. Time

  9. Average vs Instantaneous Rates of Reactions • The rate of reaction can be determined by calculating the slope of a concentration vs. Time graph. • Average rates are determined by the slope of a secant which is the change of concentration over a longer period of time. • Instantaneous rates are determined by drawing a tangent to the curve and calculating the slope of the tangent.

  10. Drawing a tangent

  11. Complete: • Thought lab on page 270, procedure 1-5 and analysis 1-4.

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