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20 Cards in this Set

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Factors Affecting Reaction Rates

Particle Size
*the smaller the particle size, the larger the surface area for a given mass of particles
-an increase in surface area increases the amount of reactant exposed for reaction
-this increases the collision frequency and therefore the reaction rate
*one way to increase surface area is to dissolve reactants
-this separates the particles and makes them more accessible to other reactants
Collision Theory
atoms, ions, and molecules can react to form products when they collide, provided that the particles have enough kinetic energy
*particles lacking the necessary kinetic energy to react bounce apart when they collide
activation energy
*the minimum amount of energy that particles must have in order to react
-acts as a barrier that reactants must cross to become products
activated complex
*the arrangement of atoms at the peak of the activation-energy barrier
-lifetime is typically about 10e-13 seconds
-very unstable: is as likely to form products as it is to re-form reactants
-also called the transition state
Factors Affecting Reaction Rates

Temperature
*Raising the temperature speeds up reactions
-directly related
*at higher temperatures, particles move faster and are more chaotic
-therefore, they have enough energy to react when they collide
-more colliding particles are energetic enough to slip over the activation-energy barrier
Factors Affecting Reaction Rates

Concentration
*cramming particles into a fixed volume increases the concentration of reactants, the collision frequency, and therefore the reaction rate
*increase in concentration=increase in reaction rate
-directly related
catalyst
substance that increases reaction rate w/o being used up itself in the reaction: allows reactions to proceed at a lower energy than is required
*catalysts lower the activation-energy barrier
*often written above the yield arrow
inhibitor
substance that interferes with the action of a catalyst
chemical equilibrium
*a state in which the forward and reverse reactions take place at the same rate
-concentrations of the components on both sides of the chemical equation are not necessarily the same
equilibrium position
*given by the relative concentrations of the system's components at equilibrium
-indicates whether the components on the left or right side of a reversible reaction are at a higher concentration
Le Chatelier's Principle
*if a stress is applied to a system in dynamic equilibrium, the system changes to relieve the stress
-stresses include concentration, temperature, and pressure
effect of Pressure on equilibrium position
Increase in pressure:
-shift moves toward lower number of moles
Decrease in pressure:
-shift moves toward higher number of moles
effect of Concentration on equilibrium position
(Pg. 542)
*removing a product always pulls a reversible reaction in the direction of products (use up reactants and achieve original ratio)
(same as removing reactants)
*adding a product always pushes a reversible reaction in the direction of reactants
*the ratio shifts in order to achieve the original 99:1 etc.

*see notecard*
effect of Temperature on equilibrium position
(ADD HEAT: SHIFT LEFT)
2SO2 + O2 = 2SO3 + HEAT
(REMOVE HEAT: SHIFT RIGHT)
equilibrium constant (Keq)

Keq= [C]c x [D]d
[A]a x [B]b
aA + bB = cC + dD

*the ratio of product concentrations to reactant concentrations at equilibrium, with each concentration raised to a power equal to the number of moles of that substance in the balanced chemical equation
*does not include solids or liquids*
rate law

Rate = k[A]a[B]b

(a and b are exponents)
*specific rate constant (K) - a proportionality constant relating the concentrations of reactants to the rate of the reaction
first-order reaction

(sum of exponents = 1st, 2nd, 3rd, etc. reaction)
*the reaction rate is directly proportional to the concentration of only one reactant
-as a first-order reaction progresses, the rate of the reaction decreases

[A]1 = first order
-initial concentration is directly related to initial rate
0.30 - 0.60
O.O80 - O.160
elementary reaction
reactions are converted to products in a single step (a one step reaction)
-has only one activated complex and thus only one activation-energy peak

# of intermediates +1 = # of elementary reactions

(count the number of arrows)
reaction mechanism
*includes all the elementary reactions of a complex reaction
-reaction progress curve resembles hills and valleys

reactant+reactant=product which then = reactant=product:

2 elementary reactions; 1 reaction mechanism
intermediate
a product of a reaction that becomes a reactant of another reaction