Chapter 7 Flashcards
Collision Theory Statements
Molecular collisions - reactant particles must collide
Activation energy - particles must posses enough activation energy
Collision Orientation - particles must come together in proper orientation
Delta H = Energy of reaction =
Hproducts - Hreactants
What if Hproducts - Hreactants is positive?
the energy of the products is higher than the energy of the reactants, so the reaction is endothermic
What if Hproducts - Hreactants is negative?
the products are lower in energy than reactants, so the reaction is exothermic
the step that requires the most activation energy determines ___
the rate of the reaction
factors that influence chemical reaction rates
physical nature of reactants,
reactant concentrations,
reaction temperatures,
presence of catalyst
Chemical kinetics rate equation
see image
Rate Law Equation
see image
R=k[A]^x • [B]^y
***the orders (exponents) must be determined experimentally
k is the rate constant, and is specific to each reaction
Keq expression for aA + bB < —> cC + dD
see image
What states of matter aren’t included in the equilibrium constant expression?
solids and liquids
factor that influences chemical equilibrium
only temperature
What if the value of Keq is large, as in 10^10
more products than reactants;
equilibrium is to the right
What if the value of Keq is between 10^3 and 10^-3
significant amounts of both reactants and products;
equilibrium is neither to the right nor the left
What if the value of Keq is small, as in 10^-10
more reactants than products;
equilibrium is to the left
There is no relationship between ___ and the value of Keq
reaction rate, because that depends on the activation energy of the forward and reverse reactions;
that determines how fast equilibrium is reached but not its position
Le Chatelier’s Principle
If stress is applied to a system in equilibrium, the system will readjust in the direction that best reduces the stress
Le Chatelier’s Principle re: temp changes
think of heat as a reactant if the reaction is endothermic
heat + reactants products
think of heat as a product if the reaction is exothermic
reactants heat + products
Le Chatelier’s Principle re: pressure changes
think of increasing pressure as increasing moles of gaseous reactant or product
look at the total number of moles of each gas (stoich)
shift eq in the direction that has less moles to relieve the pressure
if pressure is decreased, shift in the direction of ___ moles of gas to increase the pressure
if pressure is decreased, shift in the direction of MORE moles of gas to increase the pressure
if pressure is increased, shift in the direction of ___ moles of gas to increase the pressure
if pressure is increased, shift in the direction of LESS moles of gas to increase the pressure
Le Chatelier’s Principle re: concentration changes
If concentration of reactant/product is increased, shift to the opposite side to use up some of it
If concentration of a reactant/product is decreased, shift to the same side to make more of it
