module 5 - physical chemistry and transition elements Flashcards
what is short hand for concentration of reactant ‘A’
[A]
what is the correlation between rate and concentration
directly proportional
define zero order
when the concentration has no effect on rate of reaction
in a zero order reaction:
- concentration of a reactant is to the power of 0
- any number raised to the power of 0 =1
- doesn’t appear in the rate equation
- concentration does not influence the rate of reaction
in a first order reaction:
if the concentration of A is doubled (x2) the reaction rate is increased by a factor of 2^1
(directly proportional)
in a second order reaction:
if the concentration is of A is doubled, the reaction rate increases by a factor of 2^2 = x4
what is the rate equation
rate = K [A]^m [B]^n
k = rate constant
[ ] = concentration
m&n are orders
what is the trend in concentration-time graphs for:
zero order
first order
second order
zero: straight line with negative gradient
first order: downward curve with a decreasing gradient over time - half life is constant
second order: also a downward curve but steeper at the start and tails off more slowly
define exponential decay
first order reactions have a constant half life (time taken for half a reactant to be used up)
what are the trends in rate-concentration graphs for:
zero order
first order
second order
zero: straight horizontal line with zero gradient
first: straight line directly proportional
second: upward curve with increasing gradient
how can you find the rate constant (k) from rate-concentration graphs for:
zero order
first order
second order
zero - y intercept
first: gradient
second: cannot be determined
how do you work out the initial rate of reaction from a concentration-time graph
draw a tangent at T=0 and calculate the gradient
what does the rate equation only include?
reacting species involved in the rate-determining step.
what is the Arrhenius equation? And what do the letters stand for?
k = A e^(-Ea/RT)
k = rate constant
A = frequency factor
Ea = activation energy
R = gas constant (8.314)
T = temperature (Kelvin)
what is the logarithmic form of the Arrhenius equation
Ln k = - Ea/R (1/T) + Ln A
why is the logarithmic form of the Arrhenius equation useful?
so we can determine both Ea and A to be determined graphically
a plot of Ln k against 1/T gives a straight line graph in the form of y=mx+c
gradient m = -Ea/R
intercept c of Ln A on y axis
Bromine reacting with an excess of methanoic acid
Suggest how the concentration of the bromine could be monitored
Measure the reduction of colour of bromine (turns from brown-orange to colourless)
define closed system
a system in which reactants and products cannot be added or removed once the reaction begins
define dynamic equilibrium
the rate of the forward reaction is the same as the rate of the backwards reaction
define the haber process
the industrial process of making ammonia from nitrogen and hydrogen (N2g + 3H2 <–> 2NH3
list 5 reversible reactions
- haber process (N2 + 3H2 <–> 2NH3)
- disassociation of acids (HA <–> H+ + A-)
- combustion of glucose (C6H12O6 +6O2 <–> 6CO2 +6H2O)
- haemoglobin + oxygen (Hb + O2 <–> HbO2)
- ammonium chloride (NH4 + Cl <–> NH4Cl)
when can dynamic equilibrium happen?
in a closed system in a reversible reaction
how do catalysts alter equilibrium position
allows reaction to reach equilibrium faster, economically valuable
what is Le Chatlier’s principle?
when a system at equilibrium is subject to change, the system moves to minimise the effects of change
