a)
During chemical reactions, enthalpy changes occur as bonds are broken and formed.
i)
Thermal energy is needed to overcome the attractive forces between atoms. In terms of thermal energy, name the process where bonds are broken.
ii)
When bonds are formed, thermal energy is released to the surroundings. In terms of thermal energy, name the process where bonds are made.
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b)
The energy level diagram for an endothermic reaction is shown below.
Complete the diagram by labelling parts A to E.
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c)
An element X undergoes complete combustion according to the following equation. The enthalpy change, ΔH , and activation energy, Ea , for this reaction are -520 kJ mol-1 and +630 kJ mol-1 respectively. Deduce whether this reaction is exothermic or endothermic.
X + O 2 → XO 2
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d)
Define the term average bond enthalpy.
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a)
State the formula for calculating the standard enthalpy change of reaction, ΔH r
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b)
Use section 11 of the data booklet to calculate the enthalpy change, in kJ mol-1 , for the following reaction.
Cl2 + H2 → 2HCl
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c)
State whether the energy change for the reaction in part (b) is endothermic or exothermic.
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d)
Using section 11 of the data booklet, calculate the enthalpy change of reaction, ΔHr , in kJ mol-1 for the following reaction.
CH4 + Cl2 → CH3 Cl + HCl
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a)
Draw the Lewis structure of an oxygen molecule, O2 .
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b)
State the type of energy in the stratosphere responsible for the break down of the oxygen molecule.
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c)
State the equation for the formation of ozone and whether this reaction is endothermic or exothermic.
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d)
State the name of the type of compound that is responsible for the disruption of the temperature regulation in the stratosphere.
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a)
Using displayed formulae, write the equation for the reaction of ethene with water to form ethanol.
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b)
Using section 11 in the data booklet calculate the enthalpy change of reaction, ΔHr , for the reaction of ethene with water.
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c)
Define bond dissociation energy .
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