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Chemistry - Chemical Equilibrium
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Terms in this set (13)
A state in which the rates of forward and reverse reactions are the same.
An active, dynamic condition, not static.
All substances are being made & unmade at the same rate, so their concentrations are constant.
Not necessary for products and reactants to be equal.
Looks like reaction stops happening.
General Equilibrium equation
aA + bB = cC + dD
A, B are reactants
C, D are products
a, b, c, d are coefficients in the balanced equation.
Reactions that can go in either direction, from products to reactants or reactants to products.
Indicated by arrows pointing in both directions.
K eq = equlibrium constant (unitless)
K eq = Products/Reactants
Value of K eq indicates position of a reaction at equilibrium.
K eq = greater than 1 indicates products are favored - arrow points to right (products)
K eq = less than 1 indicates reactants are favored - arrow points to left (reactants)
Le Chatelier's Principle
When a stress is applied to a system at equilibrium, the equilibrium shifts to relieve the stress.
Stress: changing the concentration, pressure, volume or temp, disrupts the equilibrium and causes forward and reverse reactions to become tem
Stress (in equilibrium)
Chang in the concentration, pressure, volume or temp, that disturbs the equilibrium and causes forward/reverse reactions to become temporarily unequal.
Once equilibrium is reached, the concentrations of reactants and products are constant, and the forward/reverse reaction rates are equal.
Effects of change in concentration
Reaction will speed up in order to reach equilibrium again.
Can force a reaction by adding reactant or removing product.
Extra reactant must be used up.
Removed product must be replaces.
Increase concentration - reaction shifts to other side.
Remove (ex. product) - reaction shifts to side removed from.
Can continue to force reaction until reactants used up
Effect of change in Temp
Depends on if reaction is exothermic or endothermic
Heat shifts to side of equation w/out heat.
Exothermic reactions are favored by increase in temp.
Reactants <---- HEAT shifts
Endothermic reactions are favored by decrease in temp.
HEAT shifts ----> Products
Helpful to Include HEAT in equation:
Ex. N2 + 3H2 <---> 2NH3 + HEAT
(Exothermic - Increasing the temp, increases the heat and speeds up the reverse reaction. <---Heat shifts reaction)
Effect of change in Pressure
Influences equilibrium only if one or more substances involved is a gas.
The equilibrium shifts in the direction that decreases the number of molecules in the gas phase and thus decreases the pressure.
Ex. N2 + 3H2 <---> 2NH3
(4 moles of gas) <---> (2 moles of gas)
Reaction shifts to the side w/ 2 moles (to the right/products) to give fewer moles of gas and reduce the pressure.
Does not favor one direction of the reaction over the other.
Helps the equilibrium be reached more quickly.
Value of K eq is unchanged.
Increase in Reactant or Decrease in Product favors forward reaction.
Increase in Product or Decrease in Reactant favors reverse reaction
Increase in temp favors endothermic reaction.
Decrease in temp favors exothermic reaction.
Increase in pressure favors side with fewer moles of gas.
Decrease in pressure favors side with more moles of gas.