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RATES OF REACTION

RATES OF REACTION. (CHAPTER 6). Rate of Reaction: speed at which a chemical reaction occurs  usually expressed as the change in concentration per unit of time. Product being formed or reactant being consumed. Measurements can include mass, colour, conductivity, volume, and pressure.

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RATES OF REACTION

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  1. RATES OF REACTION (CHAPTER 6)

  2. Rate of Reaction: speed at which a chemical reaction occurs  usually expressed as the change in concentration per unit of time. • Product being formed or reactant being consumed. • Measurements can include mass, colour, conductivity, volume, and pressure.

  3. AVERAGE AND INSTANTANEOUS RATES OF REACTIONS Reaction rates are not usually constant  change with time. If we use former equation, will only get an average rate  no instantaneous.

  4. Instantaneous rate: rate of reaction at a particular time. • Do so by drawing tangent line at the point in time on a concentration-time graph. • Slope of the tangent is the instantaneous rate of the reaction.

  5. Go over the ThoughtLab on page 270. There may be something like this on the exam!

  6. Reaction Rates in Terms of Products and Reactants

  7. Just do ratios! • PPs, page 272, #1-4

  8. Independent Reading • Read the Section “Methods for Measuring Reaction Rates.” • Make brief notes. Section Review Page 276, #1-5, 7

  9. 6.2- The Rate Law: Reactant Concentration and Rate • In this section, we will study the reaction rates that are not affected by the concentration of the products. • Rate of reaction generally increases when the concentrations of the reactants increase.

  10. RATE LAW • Rate at which a reaction occurs. • k: rate constant: different for each reaction at a given temperature. • m & n: must be determined by experiment. • If m or n = 1, reaction is in ‘first order in this reactant.’ • If m or n = 2, reaction is in ‘second order in this reactant.’ • (m + n)  overall reaction order.

  11. THE RATE CONSTANT, k • Indicates the speed of a reaction. • As reaction proceeds, the reaction rate decreases because the concentration of the reactants decrease, but value of k remains constant. • Must use specific ks for each temperature.

  12. DETERMINING A RATE CONSTANT

  13. Be aware: the units associated with k may change depending on the order of the equation! As long as you calculate using your units and crossing off where applicable, you should end up with the right units! PG. 7&8

  14. The Half-Life of a Reaction • Half-life, t1/2 : the time that is needed for the reactant mass or concentration to decrease by one half of its initial value. • units are in seconds or whatever units of time are appropriate to the reaction. • Knowing the half-life of a reaction is an easy way to tell how fast or how slow a reaction occurs.

  15. The half-life of a first-order reaction • First-order reactions have a half-life that is independent of the initial concentration of the reactant. • Can be calculated using the following equation:

  16. Sample Problem • Page 286 • Carry out PPs #9-12 • Section Review: Page 288, #1-6

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