topic 7, 9, 10 - modern analytical techniques, reaction kinetics, chemical equilibrium Flashcards
(39 cards)
what is the definition of a molecular ion peak
the species that is formed when a molecule undergoes mass spectrometry and loses an electron
what is fragmentation
when a molecular ion breaks into smaller pieces
C-H bonds are never broken
what is the base peak
the tallest peak with the highest abundance
what charge do all the peaks formed from fragmentation have
1+
how do you calculate the rate of a reaction
change in concentration of either reactants of products / time for change to happen
when given a graph where concentration is on the y axis and time on the x axis, how do you work out the rate of reaction
work out the gradient
gradient = y/x
what are 2 requirements for a reaction to occur
-when 2 molecules collide they must have activation energy
-the 2 molecules must collide in the correct orientation
what is activation energy
Ea
the minimum energy that colliding particles must have for a reaction to occur
this energy is needed to break some original bonds in the reactant particles so new bonds can be made
what does ‘there is a steric factor involved in the reaction’ mean
the shape of molecules influence the reaction
what does ‘steric hinderance mean’
if a reaction suffers from steric hindrance the shape of molecules involved prevent the reaction from taking place
for example is a molecule is too large it can prevent attacking species from colliding with the necessary section of the molecule
how does increasing concentration effect rate of reaction
-there are more reactant particles present in a given volume of solution and the particles are closer together
-so more frequent succesful collisions
-so rate of reaction increases
how does increasing temperature effect rate of reaction
how does increasing pressure effect rate of reaction
-only applies to reactant molecules in gas state
-when pressure increases there are more reactant molecules in a given volume
-so more frequent successful collisions
-so higher rate of reaction
for what type of reactions does surface area effect the rate of reaction
-for heterogenous reactions involving at least 1 solid reactant, increasing the surface area of the solid increases rate of reaction
why does changing pressure have little effect on the rate of reaction when reactants are liquids or solids
-the volume of liquids and solids changes very little when pressure is increased
-so the reactants don’t move closer together
with reference to maxwell-boltzmann distribution curves, explain how changes in temperature affects the rate of a reaction
-an increase in temperature causes the curve to shift to the right and increases the fraction of molecules with activation energy
-so the frequency of successful collisions per second increases
-so rate of reaction increases
compare the collisions between reactant molecules in the gas phase and in a solution
in gas phase:
-reactant molecules are moving around at high speeds so frequently collide with one another
-if the reactant molecules collide with activation energy a reaction will occur
in a solution
-reactant molecules are closely packed so there is less space around them for movement compared to in gas phase
-in low/medium concentrations most of the solution is solvent
-solute molecules are trapped in a solvent cage
-reactant molecules come together due to diffusion into the same solvent cage, increasing the rate of collisions
-if the reactant molecules collide with activation energy a reaction will occur
what are catalysts
-increase the rate of a chemical reaction by providing an alternative pathway with a lower activation energy than the original route
-the products remain the same
-the catalyst is chemically unchanged by the end of the reaction
what are 2 economic advantages of the use of catalysts
-increase the rate of a chemical reaction, so more of the desired product is produced in a given time
-the reaction can take place at lower temperatures, so lower energy costs for the manufacturer
what type of catalysts are most commonly used in industry
heterogeneous catalysts
what are heterogenous catalysts
when the catalyst is in a different state to that of the the reactants
reaction 1 has a large enthalpy change and reaction 2 has a small enthalpy change, which reaction is most likely to be reversible
reaction 2
hydrogen and iodine react to form hydrogen iodide
hydrogen iodide can decompose into hydrogen and iodine
describe how equilibrium is established when the reaction starts with only hydrogen and iodine in a closed container
-hydrogen and iodine react to form hydrogen iodide
-as time goes on the concentration of hydrogen and iodine decreases so the rate of forward reaction decreases
-as hydrogen iodide is formed it decomposes int hydrogen and iodine
-as more hydrogen iodide is formed there is a higher concentration to be decomposed so the rate of the backwards reaction increases over time
-everntually the rate of the forward and backward reactions become equal and there is no further change in the concentration of products or reactants
-the reaction is at dynamic equilibrium
what is the definition of dynamic equilibrium
-the forward and backward reactions continuously occur at the same time
-the rates of the forward and backward reaction are equal
-the concentrations of reactants and products remain constant
