Fuels and Heats of Reactions Flashcards
What formula can be derived from Hess’s law?
ΔΗr = ΣΔΗf[products] - ΣΔΗf[reactants]
What is Hess’s law?
The heat change of a reaction is dependant on the initial and final stages of a reaction and independent of the route the reaction takes
What are hydrocarbons?
Compounds consisting ONLY of carbon and hydrogen, bonded together covalently.
What is a homologous series?
A family of organic compounds with the same general formula and similar properties and each successive member differs by a (H-C-H).
What is the difference between saturated and unsaturated molecules?
Saturated molecules contain only single bonds, while unsaturated molecules contain double or triple bonds.
What is a ‘structural isomer’?
A molecule with the same molecular formula as another molecule but a different structural formula.
Which of the following homologous series are soluble in non-polar solvents (cyclohexane)?
Alkanes, alkenes, alkynes.
All of them. They are all non-polar, and like dissolves like.
(There is little electronegativity difference, and hence polarisation, between C and H atoms, so hydrocarbons are always non-polar)
How would you demonstrate the solubility properties of alkanes, alkenes and alkynes?
Attach two syringes to a test tube of water. One is filled with the gas being tested, the other is empty of any gas (piston pushed in).
Record the extent of the gas that emerges in the second syringe.
Repeat using cyclohexane instead of water.
What is an exothermic reaction? Give an example.
A reaction where heat is given out, e.g. reaction between HCl and Mg.
What is an endothermic reaction? Give an example.
A reaction where heat is taken in (absorbed), e.g. reaction between ammonium nitrate (crystals) and water.
Define ‘heat of reaction’.
The heat in kJ released or absorbed when the number of moles indicated in the balanced equation describing the reaction react completely.
If the reaction is exothermic, will delta Hr be positive or negative?
Negative.
If it is endothermic it will be positive.
