CH 120 FNU Limiting Reactant Questions

Semester 1 Examinations 2018-2019Paper CH120-1/CH130-1
Exam Code(s)
Exam(s)
1BO, 0MB, 1BMS, 1BY, 1EH, 1 MR
Foundation Medicine, 1st Science
Module Code(s)
Module(s)
CH120, CH130
Chemistry: molecular science
Chemistry: world of the molecule
External Examiner(s)
Internal Examiner(s)
Prof. Steven Bell
Dr. Patrick O’Leary*
Instructions:
Answer question 1 and two other questions
Separate answers books are not required for each
question
Duration
Number of pages
School
2h
5 (including this front page)
Chemistry
Requirements
Marks
Graph paper, mathematical tables
All questions carry equal marks; breakdown of marks
is as shown.
Molar volume 22.4L, Avogadro’s number 6.022 x 1023
Section A
1.
Answer all parts (in your answer book) (2.5 Marks per part) in some
questions you will need to refer to the chemical equations below.
2 P + 6 H2O + 3 Br2 → 6 HBr + 2 H3PO3
H3PO3 + H2O + Br2 → 2 HBr + H3PO4
Reaction 1
Reaction 2
(i)
In reaction 1 If 2 g of P is reacted with 3g of H2O and 4g of Br2 what is
the limiting reagent?
(ii)
In reaction 1 how many g of phosphous would be required to form
3.25×1022 molecules of H3PO3?
(iii)
If reaction 1 and reaction 2 are both carried out how much HBr (mass
in g) can be prepared from 22.5g phosphorus?
(iv)
If reaction 1 and reaction 2 are both carried out how much Br 2 (mass
in g) is required if we start with 22.5g phosphorus?
(v)
If the bromine consumed in (iv) were a gas what volume would it
occupy at STP?
(vi)
Assume you allow 28.0 g of titanium chloride (molar mass = 189.7
g/mol) to react with 6.00 g of water. What is theoretical yield of
titanium oxide?
TiCl4(l) + 2 H2O(g)  TiO2(s) + 4 HCl(g)
(v)
What element has the electron configuration 1s2 2s2 2p6 3s2 3p1?
(vi)
What is the electronic configuration for the nickel2+ ion?
(vii)
Why is the atomic mass listed on periodic tables for chlorine not a
whole number?
(viii)
What type of intramolecular bonds are present in methane (CH4)?
(ix)
What type(s) of intermolecular bonds are present in oxygen gas (O2)?
(x)
What is electronegativity?
(xi)
A balloon of gas takes up 325L at 15°C. If it is heated to 80°C, what
will its new volume be?
Question continues on next page
(xii)
A car tyre has a pressure of 2.6 atm at 10°C. If the pressure inside
reaches 5 atm, the tyre will fail. How hot would the tyre have to get for
this to happen?
(xiii)
Why does pressure of a gas rise in a sealed solid container as the
temperature rises?
(xiv)
Write a rate equation for the following reaction.
H2 + I2  2HI
(xv)
For the reaction in (xiv) above, draw a diagram showing how the
concentration of all of the species would vary with time.
(xvi)
Show an energy vs reaction progression diagram for an exothermic
reaction of the following type.
A + B  C + Energy released
2.
(xvii)
Draw a 2px and a 3pz orbital in the same diagram.
(xviii)
Why is the valency of chlorine 1?
(ix)
If ΔG = ΔH –TΔS, under what circumstances of ΔH and ΔS is a
reaction definitely spontaneous?
(xx)
What purpose does ozone fulfil in the upper atmosphere?
Answer all parts
(i)
Briefly outline the factors that affect the rate of a chemical reaction.
[5 marks]
(ii)
One of the factors which effects the ozone layer is a reaction between
hydroxide radicals (HO.) and ozone (O3)
HO + O3  Products
The reaction is first order in both HO and O3.
(a) Write down the rate equation for the reaction.
[5 marks]
(b) If the rate of the reaction is 5.30 mol L-1 s-1 when
[OH] = 0.0021 mol L-1 and [O3] =0.70 mol L-1, calculate the rate
constant, k. What are the units of k?
[5 marks]
(iii)
What are the other main risks to the ozone layer?
[10 marks]
3.
Answer all parts
(i)
In an explosion a solid compound reacts to create large volumes of
gas. For example, TNT (trinitrotoluene) explodes according to the
following equation.
2C7H5(NO2)3 (s)  12CO (g) +2 C (s) + 5 H2 (g) + 3 N2 (g)
(a)
(ii)
4.
How many moles of gas are produced in the explosion of 300g
of TNT?
[10 Marks]
(b)
What volume would these gases occupy if they expanded to a
total pressure of 1 x 105 Pa (1 atm) at 25oC?
[5 Marks]
(c)
Calculate the partial pressure of each gas at that total pressure.
[5 Marks]
Carbon monoxide (CO) and hydrogen (H2) have boiling points of
-191.5oC and -253oC, respectively. A large portion of the reasoning
behind the significant difference in boiling point is due to the different
intermolecular bonding present in each gas. Discuss.
[5 Marks]
Answer all parts
(i)
What are the four quantum numbers and what information does each
one give about the characteristics of an atom or electron?
[10 marks]
(ii)
Explain how the Electron Pair Repulsion Theory (EPRT) accounts for
the shape of NH3 and NH4+
[5 marks]
(iii)
(a)
(b)
Why/how does NaCl dissolve in water?
[5 Marks]
For each bond in the molecule below identify if the bond is
covalent or polar covalent. For those that are polar covalent use
+/- notation to indicate the polarity of the bond.
[5 Marks]
5.
Answer all parts
(i)
In the recovery of iron from iron ore, the reduction of the ore is actually
accomplished by reactions involving carbon monoxide. Using the
following thermodynamical equations
Fe3O4 (s) + CO (g)  3 FeO (s) + CO2 (g) Ho+38 kJ
3Fe2O3 (s) +CO (g)  2Fe3O4 (s) + CO2 (g) Ho=-59kJ
Fe2O3 (s) + 3CO (g)  2Fe (s) + 3CO2 (g) Ho=-28kJ
(a)
Calculate Ho for the reaction:
FeO (s) + CO (g)  Fe (s) + CO2 (g)
[10 Marks]
(b)
If the So for the reaction is -23.6 J/Mol calculate the Go value at
200oC.
[5 Marks]
(c)
Is the reaction spontaneous at 200oC? Explain your answer.
[5 Marks]
(ii)
Will the entropy change for each of the following be positive or
negative?
(a)
Sugar dissolving in a cup of coffee
(b)
Moisture condensing on a cold window
[5 Marks]