Kinetics and Equilibrium review (Items 114-132 of 200 ways ..) 18. 1 Kinetics deals with the rates of chemical reactions. In chemistry, the rate of chemical change, or the reaction rate, is usually expressed as the amount of reactant changing per unit time. Equilibrium refers to the condition where forward and reverse reactions are occurring at the same rates.
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Kinetics and Equilibrium review ( Items 114-132 of 200 ways ..)
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Kinetics and Equilibrium review (Items 114-132 of 200 ways ..)
18.1
Kinetics deals with the rates of chemical reactions. In chemistry, the rate of chemical change, or the reaction rate, is usually expressed as the amount of reactant changing per unit time. Equilibrium refers to the condition where forward and reverse reactions are occurring at the same rates.
According to collision theory, atoms, ions, and molecules can react to form products when they collide with one another, provided that the colliding particles have enough kinetic energy and have the proper orientation.
>Rates of Reaction Factors Affecting Reaction Rates
Particle Size
The minute size of the reactant particles (grain dust), and the mixture of the grain dust with oxygen in the air caused the reaction to be explosive, destroying the grain elevator.
>Rates of Reaction Factors Affecting Reaction Rates
Catalysts
18.1
A reversible reaction is one in which the conversion of reactants to products and the conversion of products to reactants occur simultaneously.
When the rates of the forward and reverse reactions are equal, the reaction has reached a state of balance called chemical equilibrium. The relative concentrations of the reactants and products at equilibrium constitute the equilibrium position of a reaction. At chemical equilibrium, no net change occurs in the actual concentration of the reactants and products – i.e. concentrations are constant.
(Note this does not mean that the concentration of reactants and products are equal – avoid this common mistake).
Reversible Reactions
How do the amounts of reactants and products change in a chemical system at equilibrium?
At chemical equilibrium, no net change occurs in the actual amounts or concentration of the reactants and products.
If the rate of the shoppers going up the escalator is equal to the rate of the shoppers going down, then the number of shoppers on each floor remains constant, and there is an equilibrium.
Three stresses can cause a change in the equilibrium position of a chemical system?
•changes in the concentration of reactants or products,
•changes in temperature,
•changes in pressure (for equilibria involving gases).
18.2
The French chemist Le Châtelier proposed what has come to be called Le Châtelier’s principle: If a stress is applied to a system in dynamic equilibrium, the system changes in a way that relieves the stress.
Equilibrium ConstantsWhat does the value of the equilbrium constant, Keq , indicate about the equilibrium position of a reaction?
The equilibrium constant (Keq) is 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.
A value of Keq greater than 1 means that products are favored over reactants; a value of Keq less than 1 means that reactants are favored over products.
for Sample Problem 17.4How many joules of heat are required to melt a 10.0 grams popsicle at 0 oC. Assume that the popsicle has the same heat of fusion as water.
The quantity of heat absorbed by a melting a solid is exactly the same as the quantity of heat released when the liquid freezes; that is,
∆Hfusion = –∆Hsolidification
The quantity of heat absorbed by a vaporizing liquid is exactly the same as the quantity of heat released when the vapor condenses; that is, ∆Hvaporization = –∆Hcondensation
Heating (Endothermic) and Cooling (Exothermic) CurvesHeating versus Cooling Curves
Physical Equilibria – Saturated Solutions
Saturated solutions are another example involving physical equilibrium. The term “saturated solutions” refers to a solution containing the maximum amount of solute that will dissolve at a given temperature. The rate at which a substance crystallizes out of solution is equal to the rate at which it dissolves.