chemical equilibrium Flashcards
Chemical Equilibrium
Chemical equilibrium occurs when opposing reactions proceed at equal rates. The rate at which the products form from the reactants equals the rate at which the reactants form from the products.
At equilibrium the concentrations of all reactants and products do not change, making the reaction appear to be stopped.
Equilibrium Constant in terms of concentration (pressure)
Equilibrium-constant describes the relationship among the concentration (partial pressures) of the substances present in a system at equilibrium.
The subscript c (p) on the K indicates that concentrations (partial pressure) expressed in molarity (atmospheres) are used to evaluate the constant.
The equilibrium constant depends on the stoichiometry of the reaction. (relate your Kc to the equation)
The equilibrium constant depends on the temperature.
The equilibrium constant does not depend on the initial amounts of (initial partial pressures ) reactants and products
또다른 3가지 Equilibrium constant in terms of pressure 특징
The pressure exerted by an individual gas in a mixture is known as its partial pressure.
Assuming we have a mixture of ideal gases, we can use the ideal gas law to solve problems involving gases in a mixture.
Dalton’s law of partial pressures states that the total pressure of a gas mixture equal to the sum of the partial pressures of the component gases:
Haber Process
Ammonia-based fertilizers are required in substantial amounts in agriculture either pure ammonia or ammonium salts can be applied directly to soil.
The Haber process is a reversible reaction.
Haber process is a synthesis of ammonia from nitrogen and hydrogen:
3H2(g) + N2(g) ⇌ 2 NH3(g)
In the Haber process, nitrogen and hydrogen react at high pressure and temperature (approx. 500 °C and 200 to 600 atm in the presence of a catalyst to form ammonia.
Percent of NH3 increases with increasing pressure. Percent of NH3 decreases with increasing temperature.
magnitude of the equilibrium constant, K
If K»_space; 1
the equilibrium concentration of the products is large
The equilibrium lies to right (reaction will proceed to the right)
The products predominate
If K «_space;1
The equilibrium concentration of the reactants is large
The equilibrium lies to left (reaction will proceed to the left)
The reactants predominate
Le Châtelier’s Principle
A system in equilibrium is in balance state. If a system at equilibrium is disturbed by a concentration change, pressure or temperature, the system will shift its equilibrium position so as to counteract the effect of the disturbance.
Le Châtelier’s Principle – Change in Reactant or Product Concentration.
<3H2(g) + N2(g) ⇌ 2 NH3(g)>
If a substance is added to the system at equilibrium, the system reacts to consume some of the substance. If a substance is removed from a system the system reacts to produce more of substance.
If the concentration of reactants is increased, the equilibrium will shift to the right.
If the concentration of products is increased, the equilibrium will shift to the left.
If the concentration of reactants is decreased, the equilibrium will shift to the left.
If the concentration of products is decreased, the equilibrium will shift to the right.
Le Châtelier’s Principle – Change in Pressure.
<3H2(g) + N2(g) ⇌ 2 NH3(g)>
At constant temperature,
If the pressure is increased: volume is decreased; equilibrium moves to the side with fewer gas molecules, for Haber process, the equilibrium will shift to the RHS, producing less gas molecules
If the pressure is decreased: volume is increase, the equilibrium moves to the side with more gas molecules, for Haber the equilibrium will to the LHS, producing more gas molecules.
Le Châtelier’s Principle – Change in Temperature
For an endothermic reaction (∆H is +):
endothermic reaction requires energy, this applies to forward reaction
If we increase the temperature the equilibrium will shift to the right
If we decrease the temperature the equilibrium will shit to the left
For an exothermic reaction (∆H is -)
exothermic reaction releases energy, this applies to the forward reaction
If we increase the temperature the equilibrium will shift to the left
If we decrease the temperature the equilibrium will shit to the right
Effect of Catalyst on Equilibrium
Catalyst will lower the activation energy of reverse reaction and increase the rate of reverse reaction
However the catalyst does not have the effect on the position of equilibrium nor the equilibrium constant value since the rate of forward and reverse reactions will be increased by the same magnitude
