AP Chemistry Unit Review

Unit 7: Equilibrium

How it applies to our lives

The Haber-Bosch Process is an industrial process used to make ammonia by combining nitrogen gas from the air with hydrogen gas. Ammonia is important because it is used to make fertilizers that help crops grow and feed millions of people around the world. You may not realize but you are consuming nitrogen from the ammonia, consuming ammonia itself compared to nitrogen would be bad for us (poison). A very small amount of ammonia is added to your drinking water to help extend the disinfecting lifespan of chlorine. The Haber-Bosch Process involves chemical equilibrium and Le Châtelier's Principle in order to function. The reaction is reversible, meaning it can go forward and backward: nitrogen and hydrogen can form ammonia, but ammonia can also break back down into the original gases. Based on the Le chatelier's principle, a system which is at equilibrium will change to counteract the changes that are put on it. In a chemical industry, the yield has to be balanced and also have a fast rate of reaction. The temperature and pressure used are; 400C to 450C and 150atm to 200atm. The high temperature helps the reaction rate be more sufficient, while the high pressure favors the reaction rate and the equilibrium.

Key Vocabulary

Select a card to reveal its definition.

Common ion
Common ion effect
Le Chatelier’s principle
Equilibrium
Reversible Reaction
Equilibrium Constant
Main Takeaways
Equilibrium means that a reaction is moving forward and backwards at an equal rate. In other words it means that the forward and the reverse reactions are happening at the same speed. Although it is happening at the same rate that doesn't mean that the concentration of the products and of the reactants are the same. All it means is that the rate that the products are created is the same as the reactants are being consumed/made. The concentration of reactants and products remain constant, not equal.
The equilibrium of a reaction can shift when a reactant or product is added to the reaction. There is one solution, where everything is mixed. Adding to the solution will cause there to be a shift, although not noticeable necessarily, but there is a change in rate of a product or reactant being made. This is helpful to think about it as (there are no actual sides): If it's added to the products side of the written balanced equation, the reaction will shift to the reactants side. This happens because the system is recreating the equilibrium by creating more of the reactants, from the extra products. If it's added to the reactants side of the written balance equation, the reaction will shift to the products side. This happens because the system is recreating the equilibrium by creating more of the products, from the extra reactants.
The reaction quotient (Q)is calculated exactly like (K), but uses non-equilibrium (initial) concentrations. Comparing (Q) to (K) tells you which way a reaction will shift to reach equilibrium
The equilibrium constant (Kc) for concentration, (Kp) for partial pressure) represents the ratio of products to reactants.The formula is written as products/reactants with stoichiometric coefficients as exponents. Rule - Pure liquids(l) and pure solids (s) are never included in the equilibrium expression not variable.
A chemical process happens in multiple steps, the individual equilibrium steps link together mathematically. The overall equilibrium constant for the entire process is found by multiplying the constants of each individual step together (K overall = K1 x K2 x K3)
Common Misconceptions
Students often mistake equilibrium to mean a 50/50 split of chemicals, when it simply means the rates of the forward and reverse reactions are equal, so concentration remains constant. The rate does not change the amount. You can have 5 moles of one compound and 3 moles of another, and the reaction could still be at equilibrium. (This is also the same with other units of measure, not just mol).
Unit Quiz

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