Rates of Reaction (chapter 10 and 18) Flashcards
(50 cards)
how do you measure rate?
rate = change in concentration of reactant or product/time for change to take place
why do only a small % of collisions result in a reaction?
because they need to collide in the correct orientation and have sufficient energy to overcome activation energy
what happens if the frequency of collisions increase?
the rate of reaction also increases but the % of successful collisions stay the same
how do you increase the rate of a reaction?
increase the concentration
increase the temperature
increase the SA
what effect does increasing the concentration of reagents have?
increases the number of reactant particles in a given volume which means they’re closer together and collide more frequently, resulting in more effective collisions in a given time (same applies to pressure)
definition of orders of reaction
the power to which the concentration of the reactant is raised in the rate equation
what does a rate-concentration graph look like in a 0 order reaction?
a straight horizontal line
what does a concentration-time graph look like in a 0 order reaction?
a straight negative correlation line
what does a concentration-time graph look like in a 1st order reaction?
curved with constant half life
what does a rate-concentration graph look like in a 1st order reaction?
straight diagonal line going through the origin
what does a concentration-time graph look like in a 2nd order reaction?
deep curve
what does a rate-concentration graph look like in a 2nd order reaction?
a diagonal positive correlation
what is the rate equation?
shows the mathematical relationship between concentrations of reactants and reaction rates
rate = k [A]n
what’s the rate determining step?
a reaction may proceed in several steps (reaction mechanism) however only the slowest step controls the overall rate
what effect does increasing the surface area have on rate?
allows more collisions to occur
what effect does increasing the temperature have on rate?
this ALWAYS increases the rate as the particles have more kinetic energy so they move more quickly which increases the amount of collisions in a given temperature
what effect does increasing the temperature have on equilibrium?
shifts the boltzmann distribution curve to the right - increasing the proportion of particles that exceed Ea
particles move faster and collide more frequently
what’s the arrhenius equation?
shows the exponential relationship between the rate constant k and temperature
k=Ae -EaRT
what’s the pre-exponential factor?
accounts for frequency of collisions with the correct orientation
what’s the exponential factor?
proportion of molecules that have sufficient energy for a reaction to take place
what are 2 methods of following a progress of a reaction?
monitoring volume of gas produced
monitoring loss of mass of reactants
effect of a positive catalyst?
a substance that increases the rate of reaction by providing an alternative pathway with a lower Ea but remains itself unchanged
what’s a homogeneous catalyst?
has the same physical state as reactants and react with reactants to form an intermediate which breaks down to give the product
what’s a heterogenous catalyst?
has a different physical state and the reactant molecules are absorbed onto the surface of the catalyst then the product molecules leave the surface by deabsorbtion
