Name: le chatelier's principle in heating and cooling
Uploaded: 2020-09-24T15:06:51.000Z
Duration: 2 min 19 s
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Le Chatelier's Principle: Changing Temperature

Температура влияет на скорость химической реакции;следовательно, изменение температуры реакции в состоянии равновесия действует как напряжение в системе. Принцип Ле Шателье предсказывает, как система отреагирует, чтобы минимизировать такие возмущения. Изменение температуры меняет значение константы равновесия, в отличие от изменения концентрации или объема, которое сдвигает равновесие без изменения значения K.Рассмотрим разложение газообразного пентахлорида фосфора на трихлорид фосфора и газообразный хлор.Для этой эндотермической реакции поглощенное тепло можно рассматривать как исходное вещество. Повышение температуры увеличивает нагрев системы, как при добавлении большего количества исходного вещества. Таким образом, равновесие смещается в сторону продуктов и производит больше трихлорида фосфора и хлора, чтобы потреблять дополнительное тепло, потому что значение константы равновесия K увеличилось.С другой стороны, снижение температуры удаляет тепло из системы, подобно удалению исходного вещества. Равновесие смещается в сторону исходных веществ и производит больше пентахлорида фосфора для выделения тепла, потому что значение K уменьшилось. Для экзотермической реакции, такой как газовая реакция между диоксидом серы и кислородом с образованием триоксида серы, выделяющееся тепло можно рассматривать как продукт.Повышение температуры похоже на добавление большего количества продукта. Это смещает равновесие в сторону исходных веществ, производя больше диоксида серы и кислорода, чтобы поглотить часть добавленного тепла, потому что значение K уменьшилось. И наоборот, снижение температуры этой экзотермической реакции удаляет тепло подобно удалению продукта.Равновесие смещается в сторону продуктов и производит больше триоксида серы для выделения тепла по мере увеличения K.Таким образом, повышение температуры благоприятствует образованию продуктов эндотермической реакции, тогда как снижение температуры благоприятствует образованию продуктов экзотермической реакции.

Принцип ЛеШателье: изменение температуры

В соответствии с законом массового действия, равновесие, напряженное изменением концентрации, будет смещаться, чтобы восстановить равновесие без какого-либо изменения значения константы равновесия, K. когда равновесие смещается в ответ на изменение температуры, однако он вновь устанавливается с другим относительным составом, который показывает другое значение для константы равновесия. 
 Чтобы понять это явление, рассмотрим элементарную реакцию: 
  <img alt="Eq1" src="/files/ftp_upload/11393/11393_Equation_1.png" style="height: 50px;" />
 Поскольку это элементарная реакция, законы о ставках для переднего и заднего хода могут быть получены непосредственно из стехиометрии сбалансированного уравнения: 
  <img alt="Eq2" src="/files/ftp_upload/11393/11393_Equation_2.png" style="height: 65px;" />
 Когда система находится в равновесии, 
  <img alt="Eq3" src="/files/ftp_upload/11393/11393_Equation_3.png" style="height: 50px;" />
 Подменять законы о процентной ставке на это равенство и перегруппировать их 
  <img alt="Eq4" src="/files/ftp_upload/11393/11393_Equation_4.png" style="height: 100px;" />
 Константа равновесия может быть выражена как математическая функция констант скорости для реакций переднего и заднего хода. Поскольку константы скорости изменяются в зависимости от температуры, как описано в уравнении Аррениуса, следует иметь в виду, что константа равновесия также будет меняться в зависимости от температуры (при условии, что константы скорости изменяются в зависимости от изменения температуры). Для более сложных реакций с участием многоступенчатых механизмов реакции существует аналогичное, но более сложное математическое соотношение между константой равновесия и константами скорости шагов в механизме. Независимо от того, насколько сложной может быть реакция, температурная зависимость ее равновесной константы сохраняется. 
 Предсказание сдвига равновесие будет ощущаться в ответ на изменение температуры наиболее удобным путем с учетом изменения энтальпии реакции. Например, образование аммиака в процессе Хабрера является экзотермическим (теплопроизводящим) процессом: 
  <img alt="Eq5" src="/files/ftp_upload/11393/11393_Equation_5.png" style="height: 50px;" />
 В целях применения принципа Ле Шатье тепло, q, можно рассматривать как продукт: 
  <img alt="Eq6" src="/files/ftp_upload/11393/11393_Equation_6.png" style="height: 50px;" />
 Повышение температуры системы сродни увеличению количества продукта, поэтому равновесие будет смещаться влево. Снижение температуры в системе также приведет к смещению равновесия вправо. Для эндотермических процессов тепло рассматривается как реагент реакции и поэтому наблюдается противоположная температурная зависимость. 
 Этот текст был адаптирован к Openstax<a href="https://openstax.org/books/chemistry-2e/pages/13-3-shifting-equilibria-le-chateliers-principle">, Химия 2е изд., раздел 13.3 Сдвигающее равновесие:</a><a href="https://openstax.org/books/chemistry-2e/pages/13-3-shifting-equilibria-le-chateliers-principle"></a><a href="https://openstax.org/books/chemistry-2e/pages/13-3-shifting-equilibria-le-chateliers-principle"></a><a href="https://openstax.org/books/chemistry-2e/pages/13-3-shifting-equilibria-le-chateliers-principle"> Принцип Ле Шателье</a>.

В соответствии с законом действия масс, равновесие, налагаемое изменением концентрации, будет смещаться в сторону восстановления равновесия без каких-либо изменений в ...

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le chatelier's principle in heating and cooling

Le Chatelier's principle helps explain how chemical equilibrium responds to heating and cooling. A system at equilibrium will shift to restore balance after a temperature change, but the equilibrium constant, K, will not stay the same. Instead, the mixture reaches a new equilibrium with a different composition.

This temperature effect is different from a concentration change, which shifts equilibrium without changing K. To understand why temperature matters, the reaction can be written with forward and reverse rate laws based on the balanced equation. At equilibrium, the forward and reverse reaction rates are equal. When those rate laws are combined and rearranged, the equilibrium constant can be expressed as a function of the forward and reverse rate constants.

Because rate constants change with temperature, as described by the Arrhenius equation, the equilibrium constant can also change with temperature. This idea applies to both elementary reactions and more complex multistep mechanisms. In multistep reactions, the math is more complicated, but the temperature dependence of the equilibrium constant still remains.

A practical way to predict the direction of the shift is to use the reaction’s enthalpy change. In the Haber process, ammonia formation is exothermic, which means it produces heat. For Le Chatelier's principle, heat can be treated like a product. Raising the temperature adds heat, so the equilibrium shifts left. Lowering the temperature removes heat, so the equilibrium shifts right. For endothermic processes, heat acts like a reactant, so the temperature effect is opposite.

Le Chatelier's Principle in Heating and Cooling

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Chemical Equilibrium and Kc Rules

Chemical equilibrium and the equilibrium constant Kc describe how reactants and products are balanced in a reaction. In the oxidation of sulfur dioxide, a mixture that starts with reactants only has no product at first. As the reaction moves forward toward equilibrium, reactant concentrations decrease and product concentration increases. When equilibrium is reached, the concentrations of both stay constant. A reaction can also begin with only products present. In that case, the reaction moves...

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Shifting Equilibrium by Changing Concentration

Chemical equilibrium is a dynamic balance. At equilibrium, the forward and reverse reactions happen at equal rates. If the system is stressed in a way that changes one rate more than the other, it is no longer at equilibrium and will shift until balance is restored. This behavior is described by Le Châtelier’s principle. Changes in concentration are a major stress on an equilibrium system. Reaction rates depend mainly on concentration and temperature. For that reason, changing the amount of a...

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Gas Equilibrium Under Volume Changes

Gas-phase equilibrium can shift when the volume of the system changes. In these reactions, a change in pressure changes concentration because the partial pressure of an ideal gas is proportional to its molar concentration. That means pressure changes affect equilibrium in the same way as concentration changes. When the volume of a gas mixture changes, the concentrations of reactants and products change together. Since every gas in the equilibrium occupies the same space, the same volume change...

le chatelier's principle: changing temperature

Le Chatelier's principle helps explain how chemical equilibrium responds to heating and cooling. A system at equilibrium will shift to restore balance after a temperature change, but the equilibrium constant, K, will not stay the same. Instead, the mixture reaches a new equilibrium with a different composition. This temperature effect is different from a concentration change, which shifts equilibrium without changing K. To understand why temperature matters, the reaction can be written with...

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Estimating Equilibrium with Small Changes

A small equilibrium constant can make equilibrium calculations easier. In these reactions, the equilibrium position favors the reactants. When the initial reactant concentration is high and the Kc value is small, the change in concentration may be negligible. In that case, the equilibrium concentration is close to the initial concentration. This idea helps simplify weak acid and weak base problems. Chemists can assume that some equilibrium concentrations are equal to the initial concentrations.

key terms and concepts

Learn how heating and cooling change chemical equilibrium, why K changes with temperature, and how exothermic and endothermic reactions shift.

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Le Chatelier's Principle in Heating and Cooling

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