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U10 PT- Aanika & Mckenzie (Chemical rates (calculating reaction rates,…
U10 PT- Aanika & Mckenzie
Chemical rates
calculating reaction rates
Rate= k[A]^x [B]^y
x is the order of the reaction with respect to A
y is the order of the reaction with respect to B
Overall order= x + y
to get the x and y you need to look at the table that is provided
and do what? this section lacks detail
Reaction rates: A reaction rate is the speed at which the chemical reaction proceeds. A person can speed up a reaction by increasing the temperature, increasing the concentration, increasing the surface area, and adding a catalyst to the reaction
the collision theory: reactants must collide with sufficient energy and at the correct angle which determines the rate of the reaction. they must collide with these two things so the bonds can break
describe how changes to the nature of reactants, concentration, temperature, and surface area affect the rate of a reaction
Nature of the reactants: Some substances react ore readily than others
Concentration: When concentrations are increased, there are more particles. Increase the chances of effective collisions
Temperature: The increase in kinetic energy allows for more particles to effectively collide. A decrease in kinetic energy decreases the number of effective collisions
Surface area: Greater surface area allows particles to collide with many more particles per unit of time. Reaction rate increases
Rate laws: this is a mathematical relationship that is found by comparing reaction rates and reactant concentrations. You are given a table and you need to find the exponents that is after A and B by using this table
rate-determining step: the slowest step in a series of steps as a part of a chemical reaction. Each step will not take place at the same rate
Equilibrium
The characteristics of equilibrium is that the rate of the forward reaction has to equal the rate of the reverse reaction
Write equilibrium expressions
[C]ᶜ [D]ᵈ / [A]ᵃ [B]ᵇ
Example:
How do you solve equilibrium problems?
Calculate equilibrium constant
Keq= [C]^c
[D]^d / [A]^a
[B]^b
[C]^c and [D]^d represents the products, while [A]^a and [B]^b represent the reactants. The exponents represent each chemical species' coefficients in a balanced chemical equation
Le Chatelier's Principles
Concentration: increasing the concentration of a chemical species will make the equilibrium favor the opposite side. Ex. increasing the concentration of one of the reactants causes equilibrium to favor the products and vice versa. Decreasing the concentration of a chemical species causes the equilibrium to favor the same side. Ex. decreasing the concentration of the products causes the equilibrium to favor the products and vice versa.
Pressure (can only be used when all the chemical species are gases): Increasing the pressure will make the equilibrium favor the side with the smaller number of moles. Decreasing the the pressure causes the equilibrium to favor the side with more moles.
Temperature (requires the Delta H of formation): Increasing the temperature will cause the equilibrium to favor the endothermic reaction. Decreasing the temperature will cause the equilibrium to favor the exothermic reaction. Ex. if the delta H of formation is negative, this means the forward reaction is exothermic, which means the reverse reaction is endothermic. So when the temperaturee increases, equilibrium favors the reverse reaction.
example problems:
H2 + N2 ⇌2 NH3
Using this equation above, explain what happens if you increase the concentration of N2?
-If you increase the concentration of N2 then the equilibrium will favor the products side instead of the reactants side
Using the equation above, if the ΔHf= -875KJ/mol explain what reaction the equilibrium will favor when you increase the temperature?
-When you increase the temperature the equilibrium will favor the reverse reaction because the reverse reaction is endothermic.
Compare and contrast Le Chatelier’s principles of concentration and pressure using the balanced chemical equation above... Concentration and pressure both deal with shifts in the equilibrium, but they are both based on different things. If you increase the pressure then the equilibrium favors the side of the balanced chemical equation with fewer moles. If you increase the concentration then it favors the opposite side of the equation. If you decrease the pressure then it favors the side with more moles, and if you decrease the concentration the equilibrium favors the same side that you decreased from. Concentration can be used with any state of matter, but with pressure, all the chemical species must be a gas.
