Введение
Коэффициент скорости химической реакции
In chemical kinetics, a reaction rate constant or reaction rate coefficient (k) is a proportionality constant which quantifies the rate and direction of a chemical reaction by relating it with the concentration of reactants. For a reaction between reactants A and B to form a product C,
em=1.5|text=a A + b B → c C
where
A and B are reactants
C is a product
a, b, and c are stoichiometric coefficients,
the reaction rate is often found to have the form:
Here k is the reaction rate constant that depends on temperature, and [A] and [B] are the molar concentrations of substances A and B in moles per unit volume of solution, assuming the reaction is taking place throughout the volume of the solution. (For a reaction taking place at a boundary, one would use moles of A or B per unit area instead.) The exponents m and n are called partial orders of reaction and are not generally equal to the stoichiometric coefficients a and b. Instead they depend on the reaction mechanism and can be determined experimentally. Sum of m and n, that is, (m + n) is called the overall order of reaction.
В химической кинетике постоянная скорости реакции или коэффициент скорости реакции (k) – это константа пропорциональности, которая количественно определяет скорость и направление химической реакции, связывая её с концентрацией реагентов. Для реакции между реагентами A и B с образованием продукта C:
In chemical kinetics, a reaction rate constant or reaction rate coefficient (k) is a proportionality constant which quantifies the rate and direction of a chemical reaction by relating it with the concentration of reactants. For a reaction between reactants A and B to form a product C,
em=1.5|text=a A + b B → c C
where
A and B are reactants
C is a product
a, b, and c are stoichiometric coefficients,
the reaction rate is often found to have the form:
Here k is the reaction rate constant that depends on temperature, and [A] and [B] are the molar concentrations of substances A and B in moles per unit volume of solution, assuming the reaction is taking place throughout the volume of the solution. (For a reaction taking place at a boundary, one would use moles of A or B per unit area instead.) The exponents m and n are called partial orders of reaction and are not generally equal to the stoichiometric coefficients a and b. Instead they depend on the reaction mechanism and can be determined experimentally. Sum of m and n, that is, (m + n) is called the overall order of reaction.
a A + b B → c C,
In chemical kinetics, a reaction rate constant or reaction rate coefficient (k) is a proportionality constant which quantifies the rate and direction of a chemical reaction by relating it with the concentration of reactants. For a reaction between reactants A and B to form a product C,
em=1.5|text=a A + b B → c C
where
A and B are reactants
C is a product
a, b, and c are stoichiometric coefficients,
the reaction rate is often found to have the form:
Here k is the reaction rate constant that depends on temperature, and [A] and [B] are the molar concentrations of substances A and B in moles per unit volume of solution, assuming the reaction is taking place throughout the volume of the solution. (For a reaction taking place at a boundary, one would use moles of A or B per unit area instead.) The exponents m and n are called partial orders of reaction and are not generally equal to the stoichiometric coefficients a and b. Instead they depend on the reaction mechanism and can be determined experimentally. Sum of m and n, that is, (m + n) is called the overall order of reaction.
где
A и B – реагенты,
C – продукт,
a, b и c – стехиометрические коэффициенты,
In chemical kinetics, a reaction rate constant or reaction rate coefficient (k) is a proportionality constant which quantifies the rate and direction of a chemical reaction by relating it with the concentration of reactants. For a reaction between reactants A and B to form a product C,
em=1.5|text=a A + b B → c C
where
A and B are reactants
C is a product
a, b, and c are stoichiometric coefficients,
the reaction rate is often found to have the form:
Here k is the reaction rate constant that depends on temperature, and [A] and [B] are the molar concentrations of substances A and B in moles per unit volume of solution, assuming the reaction is taking place throughout the volume of the solution. (For a reaction taking place at a boundary, one would use moles of A or B per unit area instead.) The exponents m and n are called partial orders of reaction and are not generally equal to the stoichiometric coefficients a and b. Instead they depend on the reaction mechanism and can be determined experimentally. Sum of m and n, that is, (m + n) is called the overall order of reaction.
скорость реакции часто выражается в виде:
In chemical kinetics, a reaction rate constant or reaction rate coefficient (k) is a proportionality constant which quantifies the rate and direction of a chemical reaction by relating it with the concentration of reactants. For a reaction between reactants A and B to form a product C,
em=1.5|text=a A + b B → c C
where
A and B are reactants
C is a product
a, b, and c are stoichiometric coefficients,
the reaction rate is often found to have the form:
Here k is the reaction rate constant that depends on temperature, and [A] and [B] are the molar concentrations of substances A and B in moles per unit volume of solution, assuming the reaction is taking place throughout the volume of the solution. (For a reaction taking place at a boundary, one would use moles of A or B per unit area instead.) The exponents m and n are called partial orders of reaction and are not generally equal to the stoichiometric coefficients a and b. Instead they depend on the reaction mechanism and can be determined experimentally. Sum of m and n, that is, (m + n) is called the overall order of reaction.
Здесь k – постоянная скорости реакции, зависящая от температуры, а [A] и [B] – молярные концентрации веществ A и B в молях на единицу объема раствора, при условии, что реакция протекает по всему объему раствора. (Для реакции, протекающей на границе раздела фаз, вместо этого используют моли A или B на единицу площади.) Показатели m и n называются частными порядками реакции и, как правило, не равны стехиометрическим коэффициентам a и b. Вместо этого они зависят от механизма реакции и могут быть определены экспериментально. Сумма m и n, то есть (m + n), называется общим порядком реакции.
In chemical kinetics, a reaction rate constant or reaction rate coefficient (k) is a proportionality constant which quantifies the rate and direction of a chemical reaction by relating it with the concentration of reactants. For a reaction between reactants A and B to form a product C,
em=1.5|text=a A + b B → c C
where
A and B are reactants
C is a product
a, b, and c are stoichiometric coefficients,
the reaction rate is often found to have the form:
Here k is the reaction rate constant that depends on temperature, and [A] and [B] are the molar concentrations of substances A and B in moles per unit volume of solution, assuming the reaction is taking place throughout the volume of the solution. (For a reaction taking place at a boundary, one would use moles of A or B per unit area instead.) The exponents m and n are called partial orders of reaction and are not generally equal to the stoichiometric coefficients a and b. Instead they depend on the reaction mechanism and can be determined experimentally. Sum of m and n, that is, (m + n) is called the overall order of reaction.
Отношение к другим параметрам
Для реакции первого порядка (включая одномолекулярный одностадийный процесс) существует прямая связь между одномолекулярной константой скорости и периодом полураспада реакции: теория переходного состояния устанавливает связь между константой скорости и свободной энергией активации Гиббса – величиной, которую можно рассматривать как изменение свободной энергии, необходимое для достижения переходного состояния. В частности, этот энергетический барьер включает в себя как энтальпийные, так и энтропийные изменения, которые необходимо преодолеть для протекания реакции: Результат, полученный из теории переходных состояний, равен где h – постоянная Планка, а R – молярная газовая постоянная. В качестве практического ориентира, реакция первого порядка с константой скорости 10−4 с−1 будет иметь период полураспада (t1/2) приблизительно 2 часа. Для одностадийного процесса, протекающего при комнатной температуре, соответствующая свободная энергия активации Гиббса (ΔG‡) составляет приблизительно 23 ккал/моль.
Плазма и газы
Вычисление констант скорости процессов генерации и релаксации электронно и вибрационно возбужденных частиц имеет большое значение. Оно используется, например, в компьютерном моделировании процессов в плазменной химии или микроэлектронике. Для таких расчетов следует использовать модели, основанные на фундаментальных принципах. Это можно осуществить с помощью программного обеспечения для компьютерного моделирования.
Расчеты постоянной ставки
Константу скорости для элементарных реакций можно рассчитать с помощью моделирования молекулярной динамики. Один из возможных подходов — вычислить среднее время жизни молекулы в реакционном состоянии. Хотя это осуществимо для небольших систем с коротким временем жизни, этот подход не получил широкого распространения, поскольку реакции часто являются редкими событиями в молекулярном масштабе. Одним из простых способов преодоления этой проблемы является теория разделенного седла. Для вычисления констант скорости также были разработаны другие методы, такие как процедура Беннетта-Чандлера и Milestoning.