THE PERIODIC TABLE Flashcards
(31 cards)
HALOGENS: Does the reactivity increase from top to bottom?
No, the intermolecular forces increase from top to bottom
Halogen displacement reaction
more reactive halogen replaces other halide in aqueous solution (Redox reaction)
enthalpy
measure of the heat energy in a chemical system –> energy stored within bonds
How can enthalpy be measured?
only enthalpy change can be measured (weighing products etc.
enthalpy exothermic reaction
negative
enthalpy endothermic reaction
positive
calculating enthalpy change
q = mc deltaT (mass change, specific heat capacity, temperature change)
bond enthalpy
energy required to break bonds
–> always endothermic
Hess’ Law
and why
if a reaction can take place by two routes & starting + finishing conditions are the same: total enthalpy change is the same
why: conservation of energy
reaction rate
how fast a reactant is used up/ product formed
change in concentration/time
How can you increase the rate of reaction?
increase the rate of effective collisions:
concentration (& pressure when gases involved)
temperature
catalyst
surface area of solid components
what are effective collisions?
particles collide in the right orientation
particles have sufficient energy to overcome the activation energy
What do catalysts do?
provide alternative reaction pathway of lower activation energy
homologous catalysts
same physical state as reactants
1) catalysts react with reactants –> forms intermediate
2) intermediate breaks down –> forms products
- -> reinstalls catalyst
heterogenous catalyst
different state as reactants (usually solid)
1) reactant molecules are absorbed onto surface of catalyst
2) reaction takes place on surface
3) product molecules leave by desorption
autocatalysis
product of that reaction is a catalyst for that reaction
What does the Boltzmann distribution show?
How molecular energy levels are spread in gas particles
Important to draw Boltzmann distribution
no molecules with zero energy –> curve starts at origin
no maximum energy –> x axis not touched
area under curve = total number of molecules
How can you tell which particles can react from Boltzmann distribution?
higher energy than Ea
higher temperature Boltzmann distribution
more molecules with higher energy than Ea –> curve flattens
effects of a catalyst on collision of particles
more particles have sufficient energy to overcome Ea
–> more efficient collisions
dynamic equilibrium
equilibrium is always dynamic as forward and backward reaction both constantly take place BUT the concentrations of reactants don’t change
Le Chantelier’s principle
when a system in equilibrium is subjected to external change:
it readjusts itself to minimize effect of change
concentration LCP
equilibrium moves to side of higher amount of product
- -> reactions happen into other direction
- -> equilibrium readjusts
