Chemical Industry Flashcards
calculating order of reaction
The number on the outside of the bracket refers to the ‘order with respect to..’ and the sum of the indices of all brackets is the overall order
effect on rate
Zero order = 0 effect
First order = double concentration, double rate
Second order = double concentration, quadruple rate
nitrogen reactivity
Lack of reactivity is due to triple covalent bonds in diatomics, resulting in a high bond enthalpy
factors that can be measured to deduce order
Volumes of gasses evolved
Mass changes
pH
Colorimetry
Chemical analysis such as titration
glowing splint in dinitrogen monoxide
it will relight because the splint provides enough energy to decompose dinitrogen monoxide into nitrogen and oxygen
property of NO
Colourless
Insoluble
Turns universal indicator neutral, will turn brown very quickly in test tube if slightly exposed to oxygen due to being incredibly reactive to nitrogen dioxide
property of NO2
Brown
Soluble only in cold water
Turns indicator orange, due to acidity
property of N2O
Colourless
Slightly soluble in cold water
Neutral universal indicator, similar to nitrogen monoxide
define rate
how quickly a quantity of something changes
Rate of reaction
the rate at which reactants are converted into products
rate constant
the value of K, must always say at what temperature the changes were made
Measuring the volumes of gases evolved
Volume produced can be collected in a gas syringe
Measuring mass changes
Record the mass lost from the reaction
Ph
Monitor the pH of the reaction mixture
Colorimetry
use a colorimeter to measure the change in colour of the reaction
Chemical analysis and titration
samples of mixture are taken at regular intervals, quenching involved (stopping the reaction in the sample before analysis)
Initial rates
draw a tangent to the curve at t=0 and measure the gradient
Progress method
shows how the concentration of a reaction changes as a reaction proceeds, the gradient of each tangent gives the rate of reaction for the concentration of that substance. Then use initial rate method to plot graph of initial rate against concentration to determine order
Half life
if it is constant the reaction is first order
Reciprocal of reaction time as a measure of the rate
average rate is directly proportional to the reciprocal to 1 over time (if 1 remains constant). Plot a graph of the reciprocal against the concentration of the other substance (unconstant.)
First order
initial rate is directly proportional to concentration
second order
initial rate is directly proportional to concentration squared
zero order
rate not changing
by product and co product
the product of the unwanted side reaction
produced with the expected main amount
Change in rate if temperature is increased:
Rate equations for the two temps
Equations for K1 and K2 using Arrhenius
Calculate the values for the rest of the equation
changing the conc and pressure
Kc REMAINS CONSTANT.
They alter the composition of equilibrium mixtures but not the value of Kc itself because proportions of reactants and products alter themselves to keep the ratio in Kc expression the same.
Changing the temperature
Temperature will change Kc.
EXAMPLES: an increase in temperature to the surroundings will cause the reaction to favour the endothermic direction of the system because there will be more energy to take in.
Catalyst
Does not affect the position of equilibrium or Kc.
Only alters the rate at which equilibrium is obtained.
Does not affect the composition of the equilibrium mixture.
rate determining step
The slowest step in the mechanism
Using the rate equation in regards to RDS
The substances in the rate equation are in the RDS
Those not in the rate equation are not in the RDS
The power of the order is the number of moles in the RDS
If the energy barrier is large
the reacting species (either a single species or pair of colliding species) have enough energy to pass over it and the rate of conversion of reactants to products is low
If RDS is the first step
every step afterwards will happen very quickly
If RDS is the last step
the previous step will happen quickly and form a bottleneck because they are waiting for the product to form
how to remove a gaseous by product from the desired product
condense the desired product
define half life
the time taken for half of a certain reactant to get used up
presence of nitrite ions with iron 2 plus ions
the nitrite ions will oxidise the Fe2+ ions so the test is not reliable if the solution has nitrite ions
