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13 Cards in this Set
- Front
- Back
reversible reactions
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can occur in both the forward and reverse directions
most reactions do not go to completion-- appear to stop the rate of the reaction depends on the concentration of the reactants the rate of the forward reactions continues to decrease as the amount of reactants decreases and the rate of the reverse reaction increases until the 2 rates become equal |
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chemical equilibrium
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the state in which the forward and reverse reactions balance each other because they take place at equal rates
doesn’t mean that the amounts of the reacts and the products are equal a state of action, not inaction |
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Law of chemical equilibrium
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at a given temperature, a chemical system may reach a state in which a particular ratio of reactant and product concentrations has a constant value
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equilibrium constant
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aA + bB == cC + dD
[C]c[D]d / Keq = [A]a[B]b square brackets = molar concentrations exponents = corresponding coefficient Keq constant only at specified temp Keq >1: more products than reactants at equilibrium Keq <1: less products than reactants at equilibrium Keq will always be the same for a given reaction at a given temp, regardless of the concentrations of reactants and products |
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homogeneous equilibrium
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all reactants and products are in the same physical state
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Heterogeneous equilibrium
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reactants and products are present in multiple physical states
solids and liquids have unchanging concentrations so they can be combined with K |
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Le Chatelier’s Principle
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if a stress is applied to a system at equilibrium, the system shifts in the directions that relieves the stress
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stress
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any change in a system that upsets the equilibrium
3 types: -concentration -volume (pressure) -temp |
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concentration
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adding or removing a reactant or product shifts the equilibrium in the direction that removes the stress
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volume (pressure)
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changing the volume only shifts the equilibrium if # moles of product does not = the # moles of reactant
when you decrease the volume of a reaction vessel, you increase the pressure causing the reaction to shift to the side with the SMALLEST number of moles -opposite is also true |
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temperature
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changing the temp of a reaction at equilibrium alters both the equilibrium constant and the equilibrium position
when a reaction is exothermic (releases energy), lowering the temp shifts the equilibrium to the RIGHT b/c the forward reaction liberates heat and removes the stress TEMP DECREASE: shift TOWARDS the added energy TEMP INCREASE: shift AWAY the added energy |
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Keq
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large Keq – equilibrium mixture contains more products than reactants
small Keq – equilibrium mixture contains more reactants than products |
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Calculating the concentration of one substance in a reaction
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* the concentrations of the other substances must also be known
1. write balanced equation 2. write equilibrium constant expression 3. isolate the substance you are solving for 4. substitute all known concentrations and the value of Keq |