Energetics Revision Lesson

Energetics
Revision

Defintions

Topic 8 ​Energetics 1

Standard Enthalpy Changes of:
Reaction
Formation
Combustion
Neutralisation

Drag and Drop

The enthalpy change, $$\Delta H$$ , is the heat energy change measured at constant pressure and that standard conditions are​

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and a specified temperature, usually ​

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.

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100 kPa

298 K

100 Pa

0 K

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Standard enthalpy change of formation is the enthalpy change measured at standard conditions, when ​

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of a substance is formed from its​

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in their ​

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.

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one mole

elements

standarded states

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Standard enthalpy change of combustion is the enthalpy change measured at standard conditions when ​

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of a substance is ​

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burned in ​

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.

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one mole

completely

oxygen

incompletely

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Standard enthalpy change of neutralisation is the enthalpy change measured at standard conditions when ​

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of​

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is produced by neutralisation of an acid with an alkali.

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one mole

water

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Standard enthalpy change of atomization is the. enthalpy change measured at standard conditions when ​

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of ​

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atoms is formed from an ​

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in its standard state.

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one mole

gaseous

element

Multiple Choice

For which equation is the enthalpy change correctly described as an enthalpy change of formation?

• 2NO(g) $$\rightarrow$$  N2(g) + O2 (g)

• 2CO(g) + O2(g) $$\rightarrow$$ 2CO2(g)

• H2O(l) + NaCl (s) $$\rightarrow$$ NaCl(aq)

• K(s) + Mn(s) +2O2(g) $$\rightarrow$$  KMnO4(s)

Multiple Choice

Which equation has an. enthalpy change of reaction which corresponds to the standard enthalpy change of atomization of chlorine?

• 1/2 Cl₂(g) $$\rightarrow$$  Cl(g)

• 1/2 Cl₂(l) $$\rightarrow$$  Cl(g)

• Cl₂(g) $$\rightarrow$$  2Cl(g)

• Cl₂(l) $$\rightarrow$$  2Cl(g)

Labelling

Label the following profile for the reaction:

CaCO₃ --> CaO + CO₂

Drag labels to their correct position on the image

Products

Reactants

CaCO₃

CaO + CO₂

ΔH (positive)

ΔH (negative)

Activation Energy

Labelling

Label the following profile for the reaction:

N₂ + 3H₂ --> 2NH₃

Drag labels to their correct position on the image

Products

Reactants

ΔH (negative)

2NH₃

Activation Energy

N₂ + 3H₂

ΔH (positive)

Multiple Select

The equation for a reaction is shown.

H₂(g) + 1/2 O₂(g) → H₂O (l) ; ΔH = x kJ mol ^-1

Tick all that are correct.

• It represents enthalpy change of formation only.

• It represents enthalpy change of formation and combustion.

• x is positive

• x is negative

Multiple Choice

Which of the following processes is endothermic?

• the condensation of steam

• the freezing of water

• the decomposition of calcium carbonate into calcium oxide and carbon dioxide

• the reaction between hydrogen ions and hydroxide ions

Multiple Choice

The enthalpy change for the neutralization reaction below is − 114 kJ mol ^-1.

2NaOH (aq) + H₂SO₄(aq) ----> Na₂SO₄(aq) + 2H₂O(l)

Use this information to suggest the most likely value for the enthalpy change for the following neutralization reaction.

Ba(OH)₂ (aq) + 2HCl(aq) ----> BaCl₂(aq) + 2H₂O(l)

• − 57 kJ mol ^-1

• − 76 kJ mol ^-1

• − 114 kJ mol ^-1

• − 228 kJ mol ^-1

Multiple Choice

The enthalpy change for the neutralization reaction below is − 114 kJ mol ^-1.

2NaOH (aq) + H₂SO₄(aq) ----> Na₂SO₄(aq) + 2H₂O(l)

Use this information to suggest the most likely value for the enthalpy change for the following neutralization reaction.

NaOH (aq) + HCl(aq) ----> NaCl(aq) + H₂O(l)

• − 57 kJ mol ^-1

• − 76 kJ mol ^-1

• − 114 kJ mol ^-1

• − 228 kJ mol ^-1

Hess Cycles

Key Principle

The energy change for a reaction is the same, irrespective of the route taken, assuming the starting conditions are unaltered

Multiple Choice

• -570

• -790

• -860

• -1080

Draw

The enthalpy changes of formation of gaseous ethene and gaseous ethane are +52 kJ mol ^-1and − 85 kJ mol ^-1 respectively at 298 K.

What is the enthalpy change of reaction at 298 K for the following process?

C₂H₄(g) + H₂(g) ---> C₂H₆(g)

Construct a Hess cycle and calculate.

Making an approximation for the enthalpy change of a reaction

​Uses:

The heat energy required to break a mole of gaseous bonds homolytically in the gaseous state.

​Definition

Bond Enthalpies

​Limitations:

-bond enthalpies are averaged for all similar bonds
- energies are all in gaseous state

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Mean bond enthalpy is the enthalpy change when ​

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of a bond in the ​

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state, averaged out over many ​

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molecules, is ​

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.

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one mole

gaseous

different

broken

formed

Multiple Choice

Which one of the following statements about an endothermic reaction is correct?

• The energy absorbed in bond breaking is greater than the energy released in bond forming

• The energy absorbed in bond breaking is less than the energy released in bond forming

• The energy released in bond breaking is greater than the energy absorbed in bond forming

• The energy released in bond breaking is less than the energy absorbed in bond forming

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Bond enthalpy is the heat ​

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required to break a ​

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of bonds ​

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in the gaseous state.

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energy

mole

homolytically

heterolytically

typcial

entropy

Multiple Choice

• 221.5

• 463.5

• 588

• 927

Multiple Choice

• -95

• -208

• -1080

• -93

Drag and Drop

The enthalpy of formation of Ammonia is given as -46.1kJ/mol, the last answer (-93kJ/mol) is different for several reasons...

1) The energy change is for ​

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moles of ammonia forming, the enthalpy of ​

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is for ​

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mole forming.

2) The bond enthalpies are ​

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bond enthalpies and not ​

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to ammonia

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two

one

formation

mean

specific

three

hydrogenation

gaseous

vague

Multiple Choice

• 4.9

• 6.5

• 8.7

• 13.0

Multiple Choice

In an experiment, 1.000 g of a hydrocarbon, A, was burned completely in oxygen to produce 3.143 g of carbon dioxide and 1.284 g of water.

In a different experiment, the molar mass of the hydrocarbon, A, was found to be 84.0 g mol^–1.

A spirit burner was filled with the liquid hydrocarbon, A. The burner was weighed, lit and then used to raise the temperature of a quantity of water in a beaker, as shown in the diagram. The burner was then reweighed.

Calculate the Enthalpy of Combustion - to an appropriate number of significant figures

• -2790

• -1860

• -3650

• -8670

Multiple Choice

Using 150ml of water, and 0.717g of methanol the heat transferred to the water was 9860J, calculate the enthalpy of combustion of methanol, include a sign and appropriate number of significant figures

• -205

• -450

• -400

• +320

• +150

Dropdown

The burner lid increases the ​

Select answer

of the experiment by ​

Select answer

the amount of pentane ​

Select answer

.

Lattice Enthalpy

​Defintion

The change in heat energy when one mole of an ionic lattice is formed from its constituent gaseous ions.

e.g. Na⁺_(g) + Cl^-_(g) --> NaCl_(s)

Multiple Choice

Na⁺ (g) + Cl^- (g) --> NaCl (s)

• Ionisation

• Combustion

• Lattice enthalpy

• Atomisation

Multiple Choice

Mg (s) --> Mg (g)

• Ionisation

• Combustion

• Formation

• Atomisation

Multiple Choice

Cl (g) + e- --> Cl- (g)

• Ionisation

• Electron Affinity

• Combustion

• Formation

Multiple Choice

Mg (g) --> Mg+ (g) + e-

• Ionisation

• Combustion

• Formation

• Hydration

Multiple Choice

Na+ (g) + Cl- (g) --> Na+ (aq) + Cl- (aq)

• Formation

• Solution

• Combustion

• Hydration

Multiple Choice

½ H2 (g) + ½ Cl2 (g) --> HCl (g)

• Formation

• Combustion

• Atomisation

• Ionisation

Multiple Choice

O^- (g) + e- --> O^2- (g)

• 1st electron affinity

• 2nd electron affinity

• 3rd electron affinity

• 4th electron affinity

Multiple Choice

C (g)+ O2 (g)--> CO2 (g)

• Ionisation

• Combustion

• hydration

• solution

Multiple Choice

First electron affinity of an element is usually ________ and second electron affinity is ____________.

• exothermic, endothermic.

• exothermic, exothermic.

• endothermic, endothermic.

• endothermic, exothermic.

Multiple Choice

What enthalpy change does the number 4 represent?

• Formation

• 1^st ionisation energy of Na

• 1^st electron affinity of Na

• Atomisation of Na

Multiple Choice

Identify the enthalpy change represented by letter g.

• Enthalpy of formation

• Lattice Enthalpy

• Electron affinity of bromine

• Enthalpy of atomisation of zinc

Multiple Choice

Enthalpy change is represented by step y ?

• Enthalpy of formation calcium bromide

• Enthalpy of atomisation of calcium

• 1^st electron affinity of bromine

• Enthalpy of atomisation of bromine