topic 5: kinetics Flashcards
collision theory
for a reaction to take place, particles must collide with sufficient (enough) energy (activation energy) and the correct orientation to react
why most collisions do not lead to a reaction?
-not enough activation energy
-wrong orientation (particles not facing the right direction)
activation energy
activation energy is the minimum amount of kinetic energy required that particles need to react
- particles need this much energy to break their bonds and start the reaction
-reaction with low activation energy often happen easily, reactions with high activation energies dont as they require extra energy by heating the particles
maxwell boltzmann distribution of molecular energies in gases
-in any gas, the molecules are moving at different speeds - some move fast (lots of kinetic energy) and some move slow (less kinetic energy) but most molecules are in between
-the energy of a particle depends on its speeds so therefore, the particles have a RANGE OF ENERGIES
graph of maxwell boltzmann + draw and label
if you plot a graph of the number of molecules in a gas with the different kinetic energies - you get a curve which is the maxwell boltzmann distribution which tells us about the energy amongst the molecules
-concentration/ pressure doesnt affect it as they dont change the energy of the particles
rate of reaction
change in concentration of a reactant or product overtime
effect of temperature on reaction rate
increasing temperature, increases the rate of reaction, so a greater proportion of molecules have more kinetic energy than activation energy and be able to react, so this increases the speed of the molecules, resulting in more frequent successful collisions
temperature on a maxwell boltzmann graph + draw graph
-at higher temperatures the peak of the curve (most probable energy) is lower and moves to the right, along with the average energy. this is because MORE MOLECULES HAVE MORE ENERGY GREATER THAN THE ACTIVATION ENERGY, so molecules are moving FASTER so there is more frequent succesful COLLISONS
-a small increase in temperature can lead to a large increase in number of molecules with kinetic energy greater than activation energy which leads to a faster rate of reaction
effect of concentration on reaction rate
-increasing the concentration of a solution, increases the rate of reaction
-there are MORE PARTICLES PER UNIT VOLUME, so particles will be CLOSER TOGETHER, which result in more frequent successful COLLISIONS so they will have move chance to react so the rate of reaction increases
what happens to reaction rate as the reaction proceeds of concentration?
-as the reaction proceeds, the reactants are being used up so their concentration decreases, so the rate of reaction slows down overtime
how does concentration affect maxwell boltzmann graph?
doesnt change the maxwell boltzmann curve, as concentration has no effect on the energy of particles
effect of pressure on reaction rate
-increasing pressure of a gas, increases the rate of a reaction
-works the same as concentration - more particles per unit volume, so particles are closer together, resulting in more frequent successful collisions so the reaction rate
how does pressure affect maxwell boltzmann graph?
doesnt change the maxwell boltzmann curve, as concentration has no effect on the energy of particles
catalysts
substances that increases the rate of a chemical reaction by providing an alternative pathway with a lower activation energy, however they are not used up or chemically unchanged at the end of a reaction
effect of using a catalyst on reaction rate
-using a catalyst, increases the rate of reaction
-the catalyst provides an alternative pathway with a lower activation energy, so a greater proportion of particles have enough energy to react when they result in more frequent successful collisions per unit volume
