22 Thermochemistry: SAQ1

Hess's Law states that the heat change of a reaction depends only on the initial and final states of a reaction, and is independent of the route by which the reaction may occur.

Isomerisation is a process that converts certain compounds into more branched isomers, resulting in higher octane numbers.

Catalytic cracking breaks down large molecules into smaller ones, resulting in higher octane numbers.

<p>Dehydrocyclisation converts straight compounds into ring compounds, resulting in improved combustion characteristics.</p> Signup and view all the answers

<p>Steam reforming is a process that produces hydrogen by reacting high-temperature steam with a hydrocarbon, resulting in the production of CO and H₂.</p> Signup and view all the answers

<p>Electrolysis of water involves passing electricity through acidified water, resulting in the production of hydrogen at the cathode and oxygen at the anode.</p> Signup and view all the answers

<p>An exothermic reaction is one in which heat is given out, resulting in a negative ∆H, while an endothermic reaction is one in which heat is absorbed, resulting in a positive ∆H.</p> Signup and view all the answers

<p>The octane number is a measure of a fuel's tendency to resist auto-ignition, which is the ignition of fuel before the spark is taken in.</p> Signup and view all the answers

<p>Bond energy is the amount of energy in kJ needed to break one mole of bonds of the same type, and it affects the octane number of a fuel through the degree of branching and cyclic structure.</p> Signup and view all the answers

<p>The heat of reaction is the heat change in kilojoules when the number of moles of reactants indicated in the balanced equation react completely, while the heat of combustion is the heat change in kilojoules when one mole of a substance is completely burned in excess oxygen.</p> Signup and view all the answers

<p>The kilogram calorific value is the amount of heat energy produced per kg of fuel.</p> Signup and view all the answers

<p>The heat of formation is the heat change in kilojoules when one mole of a substance is formed from its elements in their standard states.</p> Signup and view all the answers

<p>The octane scale is based on these two compounds, with 2,2,4-trimethylpentane having an octane number of 100 and heptane having an octane number of 0.</p> Signup and view all the answers