A-Level Chemistry: Chemical Change Assignment Solutions and Analysis

This document presents a comprehensive solution to an A-Level Chemistry assignment focused on chemical change. It begins by calculating the molarity of various solutions, demonstrating the application of the molarity formula. The assignment then delves into thermochemistry, differentiating between exothermic and endothermic reactions based on their enthalpy changes, and calculating the total enthalpy change for a given reaction. Moving on to reaction kinetics, the solution determines reaction orders from rate equations and analyzes the rate of reaction with respect to the concentration of ethyl chloride. Finally, the assignment addresses chemical equilibrium, determining equilibrium constant equations for various reactions and explaining the effects of pressure, concentration, and temperature changes on equilibrium compositions, referencing Le Chatelier's principle. The solution is well-structured, providing detailed explanations and calculations for each concept covered, making it a valuable resource for students studying chemical change.

Chemical Change
(Chemistry A-Level)

Table of Contents
Section 1...........................................................................................................................................3
Calculate the molarity of a solution............................................................................................3
Section 2...........................................................................................................................................3
(A) Identify exothermic and endothermic reactions from their standard enthalpy changed data
.....................................................................................................................................................3
(B) Enthalpy change in 2Al(s) + Fe2O3(s) → Al2O3(s) + 2Fe(s):............................................4
Section 3...........................................................................................................................................4
(A) Determine the order of reaction given the rate equation......................................................4
(B) Calculate the reaction order with respect to the concentration of ethyl chloride
(CH3CH2Cl)...............................................................................................................................4
Section 4...........................................................................................................................................5
(A) For the following reactions, determine the equilibrium constant equation.........................5
(B) Explain the effect of changing pressure, concentration of a reactant or product or
temperature on the composition of a reaction mixture in equilibrium........................................6
References........................................................................................................................................7

Section 1
Calculate the molarity of a solution
Molarity can be described as number of moles of the substance per litre of the liquid. It
is used to express the concentration of the solution (Sholl and Lively, 2016).
Molarity = Moles of solutes/Volume in litres of solution
1. Molarity = 8.75 moles of NaCl/6.22 Litres = 1.407 M NaCl
2. No. of moles of NaOH = 428g*1 Mol/39.997g = 10.701 Mol
Molarity = 10.701/6.4L = 1.672 M NaOH
3. Molarity = Moles of solutes/Volume in litres of solution
Volume in litres of solution = Moles of solutes/Molarity
Volume = 4.85Mol /0.75 M = 6.467 Litres
4. Molarity of Sodium hydroxide = No. of moles of NaOH/Volume of solution in litres
No. of moles of NaOH => Density of NaOH (ρ) = Moles of NaOH/Volume of solution
=> Moles of NaOH = ρ * Volume => 2.13 * 37.0 = 78.81 Moles
Molarity of NaOH = 78.81/37.001 = 2.123 M
Section 2
(A) Identify exothermic and endothermic reactions from their standard enthalpy changed data
The chemical reactions which release energy in the form of heat, light or sound then they are
known as an exothermic reactions. They are demoted by a negative heat flow i.e. heat is lost to
the surroundings and reduction enthalpy occurs (ΔH < 0). However, some of chemical reactions
are responsible for absorbing energy in order to proceed then they are known as endothermic
reactions (Wen and et. al., 2016). These chemical reactions are characterised by positive heat
flow and increase in enthalpy (+ΔH).
1. N2 + 2O2 → 2NO2 ΔH = +68kJ mol–1
This reaction between nitrogen and oxygen is known as an endothermic chemical
reaction because it shows a positive flow of energy.
2. C3H8 + 5O2 → 3CO2 + 4H2O ΔH = -2220kJ mol–1
The reaction among propane and oxygen is termed as an exothermic chemical reaction as
it release energy and shows negative glow of enthalpy.
3. 2H2 + O2 → 2H2O ΔH = -486.3kJ mol–1

The reaction between molecules of hydrogen and oxygen to make water is considered as
an exothermic chemical reaction because of releasing energy.
4. 2CO2 → 2CO + O2 ΔH = +566kJ mol–1
This breakdown of carbon dioxide into carbon monoxide and oxygen is known as an
endothermic chemical reaction because it shows positive flow of enthalpy (Sharma, Ganesan and
Tyagi, 2016).
(B) Enthalpy change in 2Al(s) + Fe2O3(s) → Al2O3(s) + 2Fe(s):
The reaction of 2Al(s) + Fe2O3(s) → Al2O3(s) + 2Fe(s) occurs in three stages which are
mentioned below with their enthalpies.
1. 2Al(s) + Fe2O3(s) → Al2O3(s) + 2Fe(l) ΔH = -732.5kJ mol–1
2. Al2O3(s) + 2Fe(l) → Al2O3(s) + 2Fe(s) ΔH = -27.6kJ mol–1
3. Al2O3(s) + 2Fe(l) → Al2O3(s) + 2Fe(s) ΔH = -91kJ mol–1
The total enthalpy of 2Al(s) + Fe2O3(s) → Al2O3(s) + 2Fe(s) reaction:
ΔH reaction (1) + ΔH reaction (2) + ΔH reaction (3) = Total ΔH kJ mol–1
(-732.5) kJ mol–1 + (-27.6) kJ mol–1 + (-91) kJ mol–1 = -851.1 kJ mol–1
The overall enthalpy change for the given reaction of 2Al(s) + Fe2O3(s) → Al2O3(s) +
2Fe(s) has been calculated as -851.1 kJ mol–1 .
Section 3
(A) Determine the order of reaction given the rate equation
1. Rate = k[H2] [NO]2 : Order of reaction is 1 + 2 = 3 i.e. Third order reaction because it has two
Nitric oxide species with equal concentrations and one hydrogen.
2. Rate = k[H2]2 [O2] : Order of reaction is 2 + 1 = 3 i.e. Third order reaction due to having equal
concentration of two hydrogen species and one oxygen.
3. Rate = k[H2] [NO] : Order of reaction is 1 + 1 = 2 i.e. Second order reaction because both
reactants have 1 concentration.
(B) Calculate the reaction order with respect to the concentration of ethyl chloride (CH3CH2Cl)
CH3CH2Cl(g) → HCl(g) + C2H4(g)
The addition of exponents of its terms of concentration refers to order of rate law. In
context of given reaction, number of experiments with different concentration and initial rate is
given here. Experiment 1 consist 0.010 with with 1.6 x 10−8 which get increased in other

experiments according to increment in concentration. Experiment 2 shows 50% improvement in
concentration i.e. 0.015 and rate of reaction is 2.4 x 10−8. Experiment 3 indicates 3 fold
increment in concentration like 0.030 and rate of reaction is 4.8 x 10−8. Experiment 4 shows 4
fold increase in rate of reaction i.e. 6.4 x 10−8 and 0.040 in concentration of ethyl chloride.
Hence, the order of reaction has been calculated as first order in ethyl chloride (Marin,
Yablonsky and Constales, 2019).
Section 4
(A) For the following reactions, determine the equilibrium constant equation
1) CO2(g) + H2(g) CO(g) + H⇋ 2O(g)
The reaction of carbon dioxide and hydrogen to form carbon monoxide and water is an
equilibrium constant equation because it is properly balanced.
2) 2NO(g) + 2H2(g) N⇋ 2(g) + 2H2O(g)
The Chemical interaction among nitric oxide and hydrogen to given nitrogen and water
have balanced number of molecules hence equilibrium constant equation
3) Cu(s) + 2Ag+(g) Cu⇋ 2+(g) + 2Ag(s)
The reaction between copper and silver cannot considered as an equilibrium constant
equation due to not having balanced molecules at product and reactants side.
4) H2(g) + I2(g) 2HI(g)⇋
This chemical reaction can called as an equilibrium constant equation because of having
balanced molecules.
(B) Explain the effect of changing pressure, concentration of a reactant or product or temperature
on the composition of a reaction mixture in equilibrium
N2(g) + 3H2(g) 2NH⇋ 3(g)
1. Le Chatelier's Principle states that the position of an equilibrium moves to counteract the
change while a dynamic equilibrium get disturbed via changing the specific circumstances
including factors like temperature, pressure and concentration.
2. Raise in temperature
The increase in temperature is equivalent to adding excess product to the system and the
equilibrium constant decreases with increased temperature. It impacts on position of equilibrium
via changing magnitude of equilibrium constant for this reaction (Kondrat'Ev, 2016).

3. Increase in pressure
Increase in pressure on a gas phase reaction is responsible for shifting position of
equilibrium without changing magnitude of equilibrium constant.
4. Increase in concentration of nitrogen
The increase in concentration of nitrogen will also shift the position of equilibrium but
not change equilibrium constant for this reaction.

References
Books and journals
Sholl, D.S. and Lively, R.P., 2016. Seven chemical separations to change the world. Nature
News, 532(7600), p.435.
Wen, W. and et. al., 2016. Impact of emission control on PM 2.5 and the chemical composition
change in Beijing-Tianjin-Hebei during the APEC summit 2014. Environmental Science
and Pollution Research, 23(5), pp.4509-4521.
Sharma, R.K., Ganesan, P. and Tyagi, V.V., 2016. Long-term thermal and chemical reliability
study of different organic phase change materials for thermal energy storage
applications. Journal of Thermal Analysis and Calorimetry, 124(3), pp.1357-1366.
Marin, G.B., Yablonsky, G.S. and Constales, D., 2019. Kinetics of chemical reactions: Decoding
complexity. Wiley-VCH.
Kondrat'Ev, V.N., 2016. Chemical kinetics of gas reactions. Elsevier.