rate of reaction Flashcards
what is the definition of rate of reaction
-measures how fast a reactant is used up or how fast a product is formed
-or the change in concentration of a reactant over time
how to measure rate of reaction for concentration
change in concentration/ time
what factors affect rate of reaction
-temperature
-catalyst
-surface area
-concentration or preassure
what is the collision theory
two reacting particles have to collide for a reaction to occur
what is an effective collision
a collision that leads to a chemical reaction
what factors lead to an effective collision
-the particles have to collide with the correct orientation
-particles have sufficient energy to overcome the activation energy barrier of the reaction
how does increasing concentration lead to faster rate of reaction
-increases number of particles in same volume
-particles closer together and collide more frequently
-more effective collisions with correct orientation and activation energy
how does increasing preassure increase rate of reaction
-concentration of gas molecules increases as the volume the gas molecules are in is smaller
-molecles closer together and collide with correct orientation and sufficient energy
how to measure change in concentration
-monitoring decrease in concentration of reactants during reaction
-monitoring increase in concentration of products during reaction
what two methods are used to determine rate of reaction of gases
-monitoring volumes of gas at regular intervals using gas collection
-monitoring loss of mass of reactants using mass balance
what is a catalyst
- substance that changes the rate of a chemical reaction without being permanently changed
-provides an alternate reaction pathway to lower the activation energy
what two ways does catalysts speed up reactions
-provides a surface on which the reaction can take place
- react with the reactants to form an intermediate
draw an exothermic and endothermic enthalpy graph with and without a catalyst
what is a homogeneous catalyst
-has the same physical state as the reactants
how does homogeneous catalysts work
-reacts with reactants to form an intermediate which breaks down to give product and the catatylst
what is a heterogeneous catalyst
-different physical state from the reactants
how does heterogenous catalysts work
-reactant molecules absorbed into the surface of the catalyst
-reaction takes place at the surface of catalyst
-product molecules leave surface of catalyst by desorption
give 3 examples of reactions and their heterogeneous catalyst
-haber process (making ammonia)—> Fe (s)
-reforming–> Pt / Rh
-hydrogenation of alkenes–> Ni
how much chemical materials are produced using a catalyst
90%
why are catalysts sustainable
-lower activation energy
-reduces temperature and energy requirements needed for the process
-less energy–> less fossil fuels burned/less electricity used
-reduced CO2 emmisisons
why are catalysts recycled
-many catalysts contain toxic compounds–> may leech into soil if sent to landfill
-may contain valuable metals like platinum
how is the decision to recycle the catalyst or send it to landfill made
-balancing the economic and environmental factors
how do molecules in a gas move
-high speed
-collide with each other and the container they are in
-collisions are elastic–> do not slow down because of the collision and no energy lost
what is the Boltzmann
distribution
The spread of molecular energies in gases
what features are in the graph of the Boltzmann distribution
-no molecules have 0 energy–>curve starts at origin
-area under graph equal to number of molecules
-no maximum energy for a molecule–> curve never reaches the x-axis
what happens to the Boltzmann distribution graph when the temp is raised
-peak is lower and shifted to the right
-more molecules overcome activation energy
what happens to the Boltzmann distribution graph when there is a catalyst
graph shape is the same but activation energy reduced
what happens to the Boltzmann distribution graph when the preassure changes
-stays the same
