# Rates of Reaction. Read 18.1 pg. 737-738 Demonstration of variations in reaction rates: Ca vs. Na vs. Li in water to produce H 2 gas Flour burning in.

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Rates of Reaction

Read 18.1 pg. 737-738 Demonstration of variations in reaction rates: Ca vs. Na vs. Li in water to produce H 2 gas Flour burning in air 8H + + C 2 O 4 2- + MnO 4 - Mn 2+ + 4H 2 O + CO 2 H 2 SO 4, H 2 C 2 O 4 (oxalic), KMnO 4 provide ions From the list predict the fastest (1) to slowest (4)

Examples of factors affecting rate Read 18.2. For each of the 5 factors give one example from todays demonstrations Nature of reactants – Ability of the reactants to meet – The concentration of the reactants – The temperature of the system – The presence of catalysts –

Examples of factors affecting rate Nature of reactants - Na is more reactive than Ca (it more easily loses its outer electron) Ability of the reactants to meet - Flour burns faster as a fine powder because oxygen surrounds it (heterogeneous reaction?) The concentration of the reactants - reaction d has a higher H 2 SO 4 (reactant) concentration, and thus reacts faster; flour + pure O 2 The temperature of the system - reaction b is faster due to an elevated temperature The presence of catalysts - manganous sulfate (reaction c) is a catalyst for this reaction

Measuring Reaction Rates Read 18.3 (740 – 42). Answer these questions: 1.What units are associated with concentration? 2.What units are associated with reaction rate? 3.What do the square brackets in [HI] indicate (see figure 18.2, pg. 741) 4.Explain how the rate of a reaction is determined (see fig. 18.2)? 5.Plot this data (include title, axes labels): [HI] 0.1000.0720.0560.0460.0390.0340.0300.026 Time (s) 050100150200250300350

Measuring Reaction Rates 6.For the data, determine the rate of reaction at i) 25 s, ii) 175 s, and iii) 325 s. Show your work and calculations on the graph. 7.How does the rate at the beginning of a reaction compare to the rate later in a reaction? Explain why this makes sense according to one of the 5 factors that affect reaction rates (from 18.2)? 8.Explain how the rate of reaction of 2HI H 2 + I 2 is determined experimentally. 9.Do PE 2 (pg. 742)

Measuring Reaction Rates 1.Concentration: mol/L or molL –1 2.Rate = concentration/time: (mol/L)/s or molL –1 s –1 3.The square brackets "[ ]" is the symbol for concentration (mol/L) 4.The rate of reaction is measured by: Instantaneous slope; rise over run; slope of the tangent at any point.

4, 5, 6 Slope (rise/run) is the reaction rate in (mol/L)/s… rise run

Measuring Reaction Rates cont 6.i) rate (0.100-0.072)/50 = 0.00056 (mol/L)/s = 5.6 x 10 -4 molL -1 s -1 ii) rate 1.4 x 10 -4 molL -1 s -1 iii) rate 0.8 x 10 -4 molL -1 s -1 7.As the reaction proceeds, the rate decreases because reactants are being used up (recall, concentration of reactants affects rate) 8.HI concentration is measured indirectly by measuring the production of I 2 (g) (purple) – likely via a spectrometer 9.N 2 O 4 2NO 2, NO 2 forms at 0.010 molL -1 s - 1, thus N 2 O 4 decomposes at 0.005 molL -1 s -1 For more lessons, visit www.chalkbored.com www.chalkbored.com

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