To a very good approximation, the cooling of a hot body to room temperature
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Chapter 20 Solutions
PHYSICAL CHEMISTRY-STUDENT SOLN.MAN.
- Define stability from both a kinetic and thermodynamic perspective. Give examples to show the differences in these concepts.arrow_forwardExplain why half-lives are not normally used to describe reactions other than first order.arrow_forwardMany biochemical reactions are catalyzed by acids. A typical mechanism consistent with the experimental results (in which HA is the acid and X is the reactant) is Step 1: Step 2: Step 3: Derive the rate law from this mechanism. Determine the order of reaction with respect to HA. Determine how doubling the concentration of HA would affect the rate of the reaction.arrow_forward
- At 573 K, gaseous NO2(g) decomposes, forming NO(g) and O2(g). If a vessel containing NO2(g) has an initial concentration of 1.9 102 mol/L, how long will it take for 75% of the NO2(g) to decompose? The decomposition of NO2(g) is second-order in the reactant and the rate constant for this reaction, at 573 K, is 1.1 L/mol s.arrow_forwardThe Raschig reaction produces the industrially important reducing agent hydrazine, N2H4, from ammonia, NH3, and hypochlorite ion, OCl−, in basic aqueous solution. A proposed mechanism is Step 1: Step 2: Step 3: What is the overall stoichiometric equation? Which step is rate-limiting? What reaction intermediates are involved? What rate law is predicted by this mechanism?arrow_forwardWhen enzymes are present at very low concentration, their effect on reaction rate can be described by first-order kinetics. Calculate by what factor the rate of an enzyme-catalyzed reaction changes when the enzyme concentration is changed from 1.5 107 M to 4.5 106 M.arrow_forward
- Explain how a species might be part of a rate law but not part of a balanced chemical reaction.arrow_forwardThe reaction NO(g) + 1/2 Cl2(g) NOCl(g) is first-order in [Cl2] and second-order with respect to [NO]. Under a given set of conditions, the initial rate of this reaction is 620 106 mol/L s. What is the rate of this reaction if the concentration of NO is doubled and the concentration of Cl2 is reduced to half the original value? (a) 6.20 106 mol/L s (b) 124 105 mol/L s (c) 2.48 105 mol/L s (d) 4.96 105 mol/L sarrow_forwardSucrose, a sugar, decomposes in acid solution to give glucose and fructose. The reaction is first-order in sucrose, and the rate constant at 25 C is k = 0.21 h1. If the initial concentration of sucrose is 0.010 mol/L, what is its concentration after 5.0 h?arrow_forward
- The decomposition of many substances on the surface of a heterogeneous catalyst shows the following behavior: How do you account for the rate law changing from first order to zero order in the concentration of reactant?arrow_forwardAn excellent way to make highly pure nickel metal for use in specialized steel alloys is to decompose Ni(CO)4 by heating it in a vacuum to slightly above room temperature. Ni(CO)4(g) Ni(s) + 4 CO(g) The reaction is proposed to occur in four steps, the first of which is Ni(CO)4(g) Ni(CO)3(g) + CO(g) Kinetic studies of this first-order decomposition reaction have been carried out between 47.3 C and 66.0 C to give the results in the table. (a) Determine the activation energy for this reaction. (b) Ni(CO)4 is formed by the reaction of nickel metal with carbon monoxide. Suppose that 2.05 g CO is combined with 0.125 g nickel metal. Determine the maximum mass (g) of Ni(CO)4 that can be formed. Replacement of CO by another molecule in Ni(CO)4 was studied in the nonaqueous solvents toluene and hexane to understand the general principles that govern the chemistry of such compounds. Ni(CO)4(g) + P(CH3)3 Ni(CO)3P(CH3)3 + CO A detailed study of the kinetics of the reaction led to the mechanism Step1:(slow)Ni(CO)4Ni(CO)3+COStep2:(fast)Ni(CO)3+P(CH3)3Ni(CO)3P(CH3)3 (c) Which step in the mechanism is unimolecular? Which is bimolecular? (d) Add the steps of the mechanism to show that the result is the balanced equation for the observed reaction. (e) Is there an intermediate in this reaction? If so, what is it? (f) It was found that doubling the concentration of Ni(CO)4 increased the reaction rate by a factor of 2. Doubling the concentration of P(CH3)3 had no effect on the reaction rate. Based on this information, write the rate equation for the reaction. (g) Does the experimental rate equation support the proposed mechanism? Why or why not?arrow_forwardThe hydrolysis of the sugar sucrose to the sugars glucose and fructose, C12H22O11+H2OC6H12O6+C6H12O6 follows a first-order rate equation for the disappearance of sucrose: Rate =k[C12H22O11] (The products of the reaction, glucose and fructose, have the same molecular formulas but differ in the arrangement of the atoms in their molecules.) (a) In neutral solution, k=2.11011s1 at 27 C and 8.51011s1 at 37 C. Determine the activation energy, the frequency factor, and the rate constant for this equation at 47 C (assuming the kinetics remain consistent with the Arrhenius equation at this temperature). (b) When a solution of sucrose with an initial concentration of 0.150 M reaches equilibrium, the concentration of sucrose is 1.65107M . How long will it take the solution to reach equilibrium at 27 C in the absence of a catalyst? Because the concentration of sucrose at equilibrium is so low, assume that the reaction is irreversible. (c) Why does assuming that the reaction is irreversible simplify the calculation in pan (b)?arrow_forward
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