A certain substance X decomposes. Fifty percent of X remains after 100 minutes. How much X remains after 200 minutes if the reaction order with respect to X is (c) second order?
Ch.15 - Chemical Kinetics
Chapter 15, Problem 118b
Ethyl chloride vapor decomposes by the first-order reaction: C2H5Cl → C2H4 + HCl The activation energy is 249 kJ/mol, and the frequency factor is 1.6⨉1014 s-1. What fraction of the ethyl chloride decomposes in 15 minutes at this temperature?
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
First-Order Reactions
First-order reactions are chemical reactions where the rate is directly proportional to the concentration of one reactant. This means that as the concentration of the reactant decreases, the rate of reaction also decreases. The integrated rate law for a first-order reaction can be expressed as ln([A]₀/[A]) = kt, where [A]₀ is the initial concentration, [A] is the concentration at time t, k is the rate constant, and t is time.
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Arrhenius Equation
The Arrhenius equation relates the rate constant of a reaction to the temperature and activation energy. It is expressed as k = A * e^(-Ea/RT), where k is the rate constant, A is the frequency factor, Ea is the activation energy, R is the universal gas constant, and T is the temperature in Kelvin. This equation helps in understanding how temperature affects reaction rates and is crucial for calculating k when given Ea and A.
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Fraction Decomposed
The fraction decomposed in a reaction can be calculated using the integrated rate law for first-order kinetics. By rearranging the equation, one can find the concentration of the reactant at a given time and then determine the fraction that has reacted. This is important for understanding the extent of the reaction over a specified time period, such as the 15 minutes mentioned in the question.
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Related Practice
Textbook Question
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Textbook Question
The half-life for radioactive decay (a first-order process) of plutonium- 239 is 24,000 years. How many years does it take for one mole of this radioactive material to decay until just one atom remains?
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Textbook Question
Ethyl chloride vapor decomposes by the first-order reaction: C2H5Cl → C2H4 + HCl The activation energy is 249 kJ/mol, and the frequency factor is 1.6⨉1014 s-1. Find the value of the rate constant at 710 K.
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Textbook Question
When HNO2 is dissolved in water, it partially dissociates according to the equation HNO2 ⇌ H+ + NO2-. A solution is prepared that contains 7.050 g of HNO2 in 1.000 kg of water. Its freezing point is -0.2929 °C. Calculate the fraction of HNO2 that has dissociated.
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