chemistry unit 5 revision
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define first ionisation energy
 enthalpy change when one mole of gaseous atoms loses one mole of electrons to form one of mole of gaseous ions (with a single positive charge)
 X(g) > X^{+} (g) + e^{}

write an equation to represent second electron affinity
X^{} (g) + e^{} > X^{2} (g)

define lattice formation enthalpy , write an equation to show this process
 X^{+} (g) + Y^{} (g) > XY (s)
 enthalpy change when one mole of a solid ionic compound is formed from its constituent ions in the gaseous phase

write an equation to represent lattice dissociation enthalpy . how does the value of this enthalpy change differ from that of lattice formation enthalpy
 XY (s) > X^{+} (g) + Y^{} (g)
 same size as above but endothermic not exothermic

define electron affinity . write an equation to show this process
 enthalpy change when one mole of gaseous atoms gains one mole of electrons to form one mole of gaseous ions (with a single ve charge)
 X (g) + e^{} > X^{} (g)

write an equation to represent second ionisation energy
 X^{+} (g) > X^{2+} (g) + e^{}

define enthalpy of formation . write an equation to show this process
enthalpy change when one mole of a compound is formed from its constituent elements with all the reactants and products in their standard states

state hess' law
enthalpy change is independent of the route taken

define enthalpy change
heat energy change at constant pressure

explain what a born harber cycle may be used for
cycle that includes all of the enthalpy changes involved in the formation of an ionic compound therefor it can be used to calculate any one that is unknown

why is the enthalpy change for second ionisation energy larger than that of the first ionisation energy
more difficult to loose an electron from a positively charged ion  it is smaller and therefor requires more energy

why is the enthalpy change for the second electron affinity positive
negatively charged electron is being added to a negatively charged ion and therefor repulsion occurs and more energy is required

which compound has the largest lattice dissociation enthalpy LiF or csI
LiF > smaller ions therefor opposite charges approach each other more closely and more energy required

define oxidation
loss of electrons

define oxidising agent
electron acceptor

oxidation state of Cu in Cu(OH)_{2}
+2

oxidation state of V in VO_{2}^{+}
+5

Oxidation state of Cr in Cr_{2}O_{7}^{2}
+6

what is meant by a feasible or spontaneous reaction
one which takes place without input of energy

define the term entropy
randomness/disorder of a system

write an equation for a chemical reaction that involves an increase in entropy from reactants to products
explain why there is an increase in entropy
 NaHCO_{3} (s) + HCl (aq) > NaCl (aq) + H_{2}O (l) + CO_{2} (g)
 gas produced therefor arrangement of particles in product is more random

what is the symbol for entropy change
delta s

what are the units for entropy
J^{1}Kmol^{1}

explain why steam has a higher entropy value than steam
at higher temperatures H_{2}O particles spread out and are more randomly arranged compared to ordered solid

explain how the entropy change for a reaction may be calculated
delta s = sum delta s products  sum delta s reactants

a combination of which factors two factors govern the feasibility of a chemical reaction
entropy change delta s and enthalpy change

write an equation that links the two factors
delta G = delta H  TdeltaS

what value must delta G have for a reaction to be feasible
less than zero

if delta H is negative and delta S is positive what does this indicate about the feasibility of the reaction
delta G is always negative and therefor always feasible

if delta H is positive and delta S is negative what does this indicate about the feasibility of the reaction
delta G is always positive therefor the reaction is never feasible

if delta H is positive and delta S is positive what does this indicate about the feasibility of the reaction
reaction is feasible is TdeltaS is greater than delta H i.e. reaction is more likely at higher temperatures

if delta H is negative and delta S is negative what does this indicate about the feasibility of the reaction
reaction is feasible if delta H is greater than TdeltaS i.e. more likely at lower temperatures

what is significant about the temperature at which delta G = 0
in a closed system an equilibrium exists between reactants and products . can calculate the temperature at which reaction is just feasible

what can be deduced about the value of delta G when a state of change occurs and why
delta G = 0 an equilibrium exists between the two phases in the change of state

why is it useful to know the value of delta G for the reaction of metal compounds with carbon
can calculate the temperature at which the extraction of a metal from its ore just becomes feasible

why does a reaction that is thermodynamically feasible sometimes not occur at a particular temperature
doesn't tell us about kinetics of reaction  reaction may have a large activation energy

state two properties of elements sodium , magnesium and aluminium
 shiny
 conduct electricity
 react with acid to produce a salt and hydrogen

define the term rate of reaction
change in concentration of reactants and products with unit time

what are the units for rate of reaction
moldm^{3}s^{1}

in a graph of conc vs time how can the rate of reaction be determined at a particular point in the reaction
draw a tangent to the curve at the time stated and find the gradient

describe a method for monitoring the rate of a chemical reaction
colorimeter to measure the change in concentration

what is the rate equation
expression that describes how the rate of reaction depends on the concentration of the species involved (at a particular temperature) rate = K[A]^{m}[B]^{n}

define the order of reaction
the order with respect to a particular species is the power to which the concentration of that species is raised in the rate equation

define the term overall order of reaction
the sum of the powers to which the concentrations of all the species involved in the rate equation are raised

what is the symbol for the rate constant
k

write a rate equation to show an overall first order rate expression and give the units of rate constant
 rate = K[A]
 units of K s^{1}

write a rate equation to show an overall second order rate expression and give the units for the rate equation
 rate = k[a][b]
 k = mol^{1}dm^{3}s^{1}

write a rate equation to show an overall third order rate expression and give the units
 rate = k[a]^{2}[b]
 units mol^{2}dm^{6}s^{1}

what is the order of reaction with respect to x if a graph of rate of reaction vs conc of x gives a straight line
zero

what is the order of reaction with respect to y if a graph of rate of reaction vs conc of y gives a sloping straight line through the origin
first

what is the order of reaction with respect to z if a graph of rate of reaction against the conc of z gives a sloping straight line
second

what happens to the value of rate constant when temperature increases
k increases with temperature

explain your answer in terms of a maxwell botlzmann distribution curve of molecular energies and activation energy
at a higher temperature a greater proportion of molecules have energy greater than activation energy

what is meant by rate determining step
slowest step in a reaction mechanism

consider the reaction mechanism below
A > B + C (slow)
B + D > E (fast)
which is the rate determining step
A > B + C

which of the species A  E could appear in the rate equation
A

1) initial O_{2} 3x10^{3}
initial NO 2x10^{}^{3}
initial rate 6.3x10^{}^{3
}2) initial O_{2} 2x10^{3}
initial NO 1x10^{3}^{}
^{ } initial rate 2.8x10^{3}
3) initial O_{2} 1x10^{3}
initial NO 1x10^{3}^{
} initial rate 7x10^{4} use this data to calculate the order with respect to NO and NO_{2} and hence determine the overall rate equation and calculate a value for K and give its units .
 rate = k[O_{2}]^{2}[NO]
 7x10^{4}/(1x10^{3})^{2} = k = 700mol^{1}dm^{3}s^{1}