Reaction Rates

Pregunta	Respuesta
Rate =	Δ%/t = ?moldm-3
Zero order	Conc. of that reactant has NO effect on the rate
First order	Any change in conc. is mirrored in change of rate e.g. [A]^1 X 2 = rate X 2^1
Second order	Any Δ in conc. causes the rate to increase by Δ^2 e.g. [A]^2 X 4 = Rate X 4^2
Rate equation	Rate=k[A]m[B]n
Why would it be unlikely for X reaction to take place in 1 step looking at the rate equation?	Stoichiometry in reaction equation doesn't match the stoichiometry in the overall equation Collisions between more than 2 species unlikely
Overall order	overall effect of the [R]% on the rate sum of the powers
Rate constant K	Rearrange equation to make K the subject
K from overall order =1	Rate=k[A]1 K=rate/[A]1 moldm-3s-1/moldm-3 K=moldm-3
Methods to produce conc.-time graphs	Continuous monitoring via gas collection/mass loss/colorimetry
Analysis by Colorimetry (8)	1. Prepare STD sol. of known % of coloured chemical. 2. Select a filter w/ comp. colour to coloured chem. 3. Zero the colorimeter with water 4. Measure the absorbance readings of the STD sol. 5. Plot a calibration curve of absorbance against %. 6. Carry out reaction, take absorbance readings at measured intervals. 7. Use the calibration curve to measure the conc. of coloured chem at each absorbance reading. 8. Plot a conc.-t graph to determine r.o.r
Purpose of calibration curve	Get concentration of reactant from absorbance reading
r.o.r from C-t graphs	Gradient
Orders from C-t graphs	Zero First
Zero order	Straight line w/ negative gradient R.O.R doesn't change during reaction
K from zero order reaction	K=gradient
First Order	Downward curve w/ decreasing gradient over time Constant t1/2 for [reactant]
t1/2	t for [r] to halve from its original value
t1/2 First Order	Constant Shows Exponential Decay
K from First Order	K= ln2/t1/2 OR K= Rate(y/x)/[Reactant]
t1/2 from K	t1/2 = ln(2/k)
Rate-% graphs	Can be plotted for rate measurements at different concentrations
Orders from rate-% graphs	Zero - horizontal straight line w/ zero gradient r.o.r independent of conc. change
K from zero order reaction	r = K Intercept on Y axis gives K
First order	Straight line through origin
Rate from First Order rate-%	R=k[A] k = rate/% = Y/X
Second order graph	Upward curve w/ increasing gradient
Determing K from 2nd order rate-% graph	Plot 2nd graph of rate against [ ]^2 to get a straight line through origin Gradient of straight line = K
Clock reaction is a method of obtaining	IR by T for colour/precipitate formation
IR=	1/t
Iodine clock colour change	Iodine w/ starch Colourless -> blue-black
Procedure	Keep [I-] constant, vary other [ ] Keep [I-] constant, vary [ ] Plot graph of 1/t against conc.
Rate-determining step	Slowest step
What species are included in the slowest step?	Species in the rate equation
What do the orders match?	The no. of species involved in the RDS
Hydrolysis of haloalkane	RBr + OH- --> ROH + Br- Step 1: RBr --> R+ + Br- Step 2: R+ + OH- --> ROH Step 3: RBr + OH- ---> ROH + Br-
Effect of T on rate constants	T ^ = Rate ^ = K^
^10c	For many reactions doubles r/k
Graph showing ^ effect	K T Upward curve
Effects of ^T (2)	^T = Particles move faster, more collisions. ^T = More particles w/ Ea.
Arrhenius equation, exponential form	K=A e^-(Ea/RT) R=8.314 jmol-1k-1
A	Factor that takes into account f of collisions w/ correct orientation
e^-Ea/RT	Proportion of particles w/ enough E to succeed Ea
Arrhenius equation - graphical form	lnK = -Ea/RT + lnA y = m x + c
Y = MX + C	Y = y axis X = x axis M = gradient C = intercept at Y
A	A = e^ln A
Ea	Ea * R

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