Assignment Brief This assignment is to be completed independently. You will need a periodic table and a calculator. LO1 Understand enthalpy changes associated with exothermic and endothermic reactions...

Assignment Brief

This assignment is to be completed independently. You will need a periodic table and a calculator.

LO1 Understand enthalpy changes associated with exothermic and endothermic reactions

AC 1.1 Interpret enthalpy profile diagrams for exothermic and endothermic reactions including the concept of activation energy, E_A

AC 1.2 Define standard conditions and standard enthalpy changes of combustion, formation and reaction.

AC 1.3 Calculate enthalpy changes of reaction from average bond enthalpy values or experimental data

AC 1.4 State Hess’ Law and use enthalpy cycles to indirectly determine enthalpy changes

1. a) Describe the difference between exothermic and endothermic reactions.

b) Define activation energy.

c) Draw a labelled enthalpy profile diagram for an endothermic reaction.

2. a) State the standard conditions used when considering enthalpy changes.

b) Give the notation for and define the following standard enthalpy changes:

i) the standard enthalpy change of formation

ii) the standard enthalpy change of combustion

iii) the standard enthalpy change of reaction.

c) Write equations for the following enthalpy changes:

i) the standard enthalpy change of formation of propan-1-ol, (C₃H₇OH)

ii) the standard enthalpy change of combustion of propan-1-ol, (C₃H₇OH)

iii) the standard enthalpy change of formation of water, (H₂O)

iv) the standard enthalpy change of combustion of octane, (C₈H₁₈)

3. a) Calculate the enthalpy change of combustion of propane (C₃H₈) using the bond enthalpies below:

b) Calculate the enthalpy change of formation of ammonia (NH₃) using the bond enthalpies below:

4. a) The enthalpy change of combustion of hexane was measured using a calorimeter containing 200 cm³ of water; 0.5g of hexane (C₆H₁₄) was burnt. The temperature of the water increased by 28 K.

Calculate the enthalpy change of combustion of hexane.

(c=4.18 Jg ^-1K^-1). Give your answer in kJ mol^-1.

b) Suggest why this experimental value is less than the standard enthalpy change of combustion of hexane found in a data book.

5. a) State Hess’ law.

b) Use a Hess cycle to calculate the enthalpy change of formation of butane (C₄H₁₀) using the data below:

c) Use a Hess cycle to calculate ∆_rH^Ɵ for the following reaction using the data provided:

NH_3(g) + HCl_(g) NH₄Cl_(s)

LO2 Understand the factors that affect the rate of a chemical reaction

AC 2.1 Apply the collision theory to explain the factors that affect the rate of a reaction

AC 2.2 Analyse the Maxwell Boltzmann distribution curve to explain the effect of temperature on the rate of a reaction

1. a) Define the term ‘rate of reaction’

b) Apply your understanding of the collision theory to describe and explain the factors that affect the rate of a chemical reaction.

2. Below is a Maxwell Boltzmann distribution curve for a sample of gas at a fixed temperature. E_Ais the activation energy for the decomposition of this gas.

No. of molecules

with a given energy

energy E_A

(a) Copy this diagram and add the distribution curve for the same sample of gas at a higher temperature.

(b) Use the Maxwell-Boltzmann distribution to explain the effect of increasing temperature on the rate of a chemical reaction.

(c) What does the area under the curve represent?

(d) Use your diagram of the Maxwell-Boltzmann distribution to show and explain the effect of adding a catalyst to the rate of a chemical reaction.

LO3- Apply Le Chatelier’s principle to explain the effects of changes in conditions on a system in dynamic equilibrium

AC 3.1 State Le Chatelier’s principle and apply it to explain the effects of changing conditions on the position of equilibrium.

1. a) What does it mean when a system is described as being at dynamic equilibrium?

b) State the conditions needed for a dynamic equilibrium to be established.

c) State Le Chatelier’s Principle

2. The reaction between water and carbon monoxide will reach dynamic equilibrium:

H₂O_(g) + CO_(g) ⇌ H_2(g) + CO_2(g) ∆H = -42.1 kJ mol^-1

Use Le Chatelier’s principle to state and explain the effect on the concentration of hydrogen in the equilibrium mixture if the following changes are made:

i) The concentration of CO_(g) is increased

ii) The temperature is decreased

iii) The pressure is increased

3. Use at least one example to explain why, in industrial processes that involve equilibria, a compromise of temperature and pressure conditions is used.

LO4 Understand the theory and reactions of acids and bases

AC 4.1 Define acids and bases using the Bronsted-Lowry theory

AC 4.2 Explain how the pH scale is used to measure acidity and alkalinity

AC 4.3 Explain the reactions of acids with alkalis, a metal and a carbonate

1. a) What are the Bronsted-Lowry definitions of

i) an acid?

ii) a base?

b) What is an alkali?

c) Identify the acids and bases in the following reactions:

i) HCl_(aq) + NaOH_(aq) NaCl_(aq) + H₂O_(l)

ii) NH_3(aq) + H₂O_(l) NH₄⁺_(aq) + OH^-_(aq)

d) Explain what the pH scale represents and describe how it is used to measure acidity and alkalinity.

e) Use examples to explain the difference between strong and weak acids.

2. Write full chemical equations for the following reactions and describe any changes that you would see:

i) The reaction between nitric acid and aqueous potassium hydroxide.

ii) The reaction between hydrochloric acid and solid calcium carbonate.

iii) The reaction between sulphuric acid and aqueous sodium hydroxide.

iv) The reaction between magnesium and hydrochloric acid.

v) The reaction between hydrochloric acid and ammonia.

vi) The reaction between ethanoic acid and aqueous sodium hydroxide.

vii) The reaction between zinc and nitric acid.

LO5 Understand simple redox processes

AC 5.1 Explain oxidation and reduction in terms of electron transfer and changes in oxidation states.

AC 5.2 Assign oxidation states to atoms in compounds and ions.

1. Define the terms ‘oxidation’ and ‘reduction’ in terms of electron transfer and changes to oxidation states.

2. a) State the oxidation states of all the elements in the following compounds:

i) HCl

ii) H₂S

iii) CH₄

iv) MgBr₂

v) NaClO₃

vi) K₂SO₄

b) State the oxidation states of the elements in the following ions:

i) OH^-

ii) CO₃^2-

iii) ClO₄^-

iv) PO₄^3-

3. a) Define the term ‘redox’

b) Do the following processes involve oxidation, reduction, both oxidation and reduction or

none of these?

i) Mg Mg²⁺ + 2e^-

ii) Zn + Cl₂ ZnCl₂

iii) Ag⁺ + Br^- AgBr

iv) 2H⁺ + 2e^- H₂

4. a) For the following redox reaction identify which element is oxidised, which element is reduced; the oxidising agent and the reducing agent. Include the oxidation states of each atom or ion before and after the reaction.

2Fe + 3Cl₂ 2FeCl₃

b) Balance the two half equations below then combine them to give the overall equation for this reaction, explain why this is a redox reaction.

Zn Zn²⁺

Cu²⁺ Cu