Download 1 Q. If ΔrH is positive, what can you say about the reaction? 2 Q If

1 Q. If ΔrH is positive, what
can you say about the
reaction?
1 A. That the reaction is
endothermic when proceeding
in the left to right direction as
written.
2 Q If ΔrH is negative, what
can you say about the
reaction?
2A
That the reaction is
exothermic when proceeding in
the left to right direction as
written.
3 Q For an exothermic
reaction, what can you say
about the enthalpy of
products of the reaction when
compared to the enthalpy of
the reactants?
3A
That the products have
less enthalpy (energy) than the
reactants.
4 Q For an endothermic
reaction, what can you say
about the enthalpy of
products of the reaction when
compared to the enthalpy of
the reactants?
4A
That the products have
more enthalpy (energy) than
the reactants.
5 Q In terms of activation
energy, what is the effect of a
catalyst on a reaction, and
how does it do this?
5A
A catalyst lowers the
activation energy for a reaction by
providing an alternative reaction
pathway for the reaction.
6 Q When ammonium
nitrate dissolves in water, an
endothermic reaction takes
place. What would you
observe to happen, and what
is happening?
6A
The solution would cool
down (and so its container
would get cold) because it is
absorbing energy from its
surroundings.
7 Q When potassium
hydroxide dissolves in water,
an exothermic reaction takes
place. What would you
observe to happen, and what
is happening?
7A
The solution would heat
up (and so its container would
get hot) because it is releasing
energy from its surroundings.
8 Q What is the unit of
Enthalpy?
8A
J, or kJ, or J mol-1 or kJ
mol-1.
9 Q For the reaction
C(s) + O2(g) Æ CO2(g)
ΔrH = -400 kJ/ mol-1.
How much heat would be released
when 88 g of CO2 is produced?
Where do we commonly see this
reaction used?
9A
MCO2 = 44, so 2 moles
produced, so 400 kJ heat
produced. A common use of
this reaction is in charcoal
BBQs.
10 Q. In terms of reactants
and products, what happens in
a reaction which is in dynamic
equilibrium?
10 A. The forward and
background reactions are going
on continuously but at the
same rate, so no change is
observed.
11 Q. How would you
distinguish a process which is
in physical equilibrium with
one which is in chemical
equilibrium?
11 A. In a physical process the atoms
or molecules are not altered, only
their physical state is. In a chemical
process the atoms or molecules are
changed into different combinations.
12 Q. Is the dissolution of an
ionic salt in water a chemical
or physical process?
12 A. Chemical as the bonds in
the salt are broken and
hydrolysed ions are formed.
13 Q. What happens to the
concentrations of all species
in a system which is in
dynamic equilibrium?
13 A. Nothing, they stay the
same.
14 Q. What is the equilibrium
constant for the reaction:
H2(g) + I2(g) Ù 2HI(g)?
14 A.
15 Q. What is the equilibrium
constant for the reaction:
N2(g) + 3F2(g) Ù 2NF3(g)?
15 A.
Kc = [HI]2/[H2][I2]
Kc = [NF]2/[N2][F2]3
16 Q. What is the value of [C]
in the equilibrium constant
expression for the reaction
and what is Kc:
C(s) + O2(g) Ù CO2(g)?
16 A. 1, so it doesn’t appear in
the expression.
so Kc = [CO2]/[O2]
17 Q. What is the effect of an
increase in pressure in the
reaction:
2NO2(g) Ù N2O4(g) + heat?
17 A. Equilibrium moves to the
right i.e. more N2O4 forms.
18 Q. What is the effect of an
increase in temperature in the
reaction:
2NO2(g) Ù N2O4(g) + heat?
18 A. Equilibrium moves to the
left i.e more NO2 forms.
19 Q. What is the effect of an
increase in [N2O4] in the
reaction:
2NO2(g) Ù N2O4(g) + heat?
19 A. Equilibrium moves to the
left i.e. more NO2 forms.
20 Q. What is the effect of an
increase in [NO2] in the
reaction:
2NO2(g) Ù N2O4(g) + heat?
20 A. Equilibrium moves to the
right i.e. more N2O4 forms.
21 Q. For the reaction
21 A.Kc = [CH3COO-][H3O+]/[CH3COOH]
CH3COOH + H2O Ù CH3COO- + H3O+
Kc = 1.8 x 10-5
If [CH3COOH] = 0.1 mol L-1,
then what is [CH3COO-]?
= 1.8 x 10-5
[CH3COO-] = [H3O+]
So [CH3COO-]2 = √(1.8 x 10-5/0.1)
And [CH3COO-]= 4.24 x 10-3
22 Q.
a. What is an acid?
b. What is the definition of
pH?
22 A.
a. A proton donor.
b. pH = -log[H3O+]
23 Q. What is a base?
What is the formula for Kw and
what is its value?
23 A.
a. A proton acceptor.
b. Kw = [H3O+][OH-] = 10-14
24 Q. Define a weak and a
strong base and explain how
they differ from concentrated
and dilute bases.
24 A.
A weak base does not completely
dissociate in reaction with water: a strong one
does. A concentrated base has more of the
base dissolved in water than a dilute one, but
has nothing to do with the extent of
dissociation.
25 Q. Explain why the
ammonium ion is acidic.
25 A. The ammonium ion reacts with
26 Q. Explain why ammonia is
basic.
26 A. Ammonia reacts with
water to produce an hydroxide
ion.
NH3 + H2O Ù NH4+ + OH-
27 Q. Explain why
a. the salt Na2CO3 is basic,
b. the salt NH4Cl is acidic.
27 A.
water to produce an hydronium ion.
NH4+(aq) + H2O Ù NH3(aq) + H3O+(aq)
A proton is transferred from the
ammonium ion to the water
molecule.
a. NaOH is a strong base, H2CO3 is a
weak acid, so the base dominates to give a
basic solution in water.
b. HCl is a strong acid but NH4OH is a weak
base so the acid dominates to give an acidic
solution in water.
28 Q. What is the pH of a
0.05 mol L-1 solution of
sulfuric acid in water?
28 A. pH = 1
29 Q. What is the pH of a
0.0025 mol L-1 solution of
nitric acid?
29 A. pH = 2.6
30 Q. What is the [OH-] in
a solution of 0.001 mol L-1
HCl?
30 A. [OH ] = 10
-
-11
mol L-1