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Topic 6, 7, 8, 9 Chemistry Test

Topic 7: Equilibrium

Equilibrium: the condition in which the concentrations of reactants and products stop changing; when therate of the forward reaction is equal to the rate of the reverse reaction

Forward reaction = Reverse reaction

-When there is a lot of reactant left, you say it is favored for the reverse reaction-When there is a higher concentration of products, you say it the forward reaction is favorable to occur 

The Equilibrium Constant: K c -The value of Kc tells you whether the forward or reverse reaction is favored

Kc >>1 Equilibrium constantis MUCH greater than

one

Equilibrium lies to the rightProducts are favored

Kc is very large The reaction has gone to completion

Kc > 1 Equilibrium constant

is slightly greater than

one

The reaction has not gone to completion

Kc << 1 Equilibrium constant

is much less than one

Equilibrium lies to the left

Reactants are favored

Kc is very small Reaction can be considered not to occur 

-Equilibrium constant does not depend on:

-Initial or final concentration

-Whether or not any other substances are present as long as they do not react with any of the other 

products or reactants-Equilibrium constant is ONLY affected by temperature

-Two types of equilibriums

1. Homogeneous: all reactants and products in the same phase2. Heterogeneous: when they are in different phases

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LE CHATLIER¶S PRINCIPLE

-If a system is disturbed by a change in temperature, pressure, or concentration of one of its components,

the system will shift its equilibrium position so as to counteract the effect of the disturbance.

1. Changing concentration of a reactant or product-When you increase concentration of a reactant or product, it will shift in the oppositedirection of what was removed

-When you remove some reactant or product, it will shift in the direction of what was

removed

2. Change in volume and pressure

-System wants to reduce additional pressure

-Pressure caused by collisions of molecules on wall of container 

-Way to reduce particles: reduce collisions-Remove particles to reduce pressure

-Equilibrium will shift towards the side that produces fewer moles of gas

-When you increase pressure in a system of equilibrium, the system will respond by

reducing the number of colliding particles by shifting towards the side that makes thefewer number of particles (measured in moles)

-Change in pressure does not influence the value of the equilibrium constant*An increase in pressure is the same as a decrease in volume*A decrease in pressure is the same as an increase in volume

3. Effect of changing the temperature

-Changing the temperature will have different effects on an endothermic or exothermic

reaction. Be sure to identify which kind it is before writing your answer -In an exothermic reaction, heat is a product:

aA + bB cC + dD + heat

-In an endothermic reaction, heat is a reactant:

heat + aA + bB cC + dD-For an exothermic reaction, adding heat will cause equilibrium to shift in the oppositedirection-For an endothermic reaction, adding heat will cause equilibrium to shift to the right

-For an exothermic reaction: increase in temperature = decrease in value of Kc

decrease in temperature = increase in value of Kc

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-For an endothermic reaction: increase in temperature = increase in value of Kc

decrease in temperature = decrease in value of Kc

-Effect of a catalyst:

-Reduces activation energy in both directions-Lets a system reach equilibrium faster with no shift in equilibrium-No change or effect on value of Kc

The CONTACT PROCESS

-Makes sulfur dioxide

-Converts sulfur dioxide into sulfur trioxide

By increasing proportion of oxygen you can increase sulfur trioxide

1:1 ratio gives best results

The Temperature:

-You need as low a temperature as possible to get maximum results

-BUT low temperature reduces rate of reaction hugelyThe Pressure:

-Increase in pressure produces best results-BUT high pressure is expensive to maintain

The Catalyst:-The catalyst does not affect equilibrium at all

-Needs catalyst to make reaction efficient

THE HABER PROCESS

The Temperature:

-Production will be favored if you lower the

temperature, but that hugely decreases rate of 

reaction

The Pressure:

-Works best at high pressure, but that is too

expensive to maintain-Has to make a compromise