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| Question | Answer |
| What is the general formula for alkanes? | CₙH₂ₙ₊₂ |
| Are alkanes saturated or unsaturated compounds? | Saturated |
| Describe the structure of cycloalkanes | Cycloalkanes have a ring of carbon atoms with two hydrogens attached to each carbon |
| What is the general formula for cycloalkanes? | CₙH₂ₙ |
| TRUE OR FALSE: Cycloalkanes are saturated compounds | TRUE Cycloalkanes contain only single C-C bonds but they are still considered saturated |
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Name this compound:
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3,4-diethylheptane |
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Name this compound:
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4-ethyl-5-propyloctane |
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Name this compound:
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3,4-dimethyl-4,5-diethyl-5-propyloctane |
| What is the shape of an alkane molecule? |
Tetrahedral
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| What is the bond angle around each carbon? | 109.5° |
| In alkanes, what type of bond exists between carbon atoms, and between carbon and hydrogen atoms? | Sigma (σ-) bond |
| How are σ-bonds formed? |
Atomic orbitals on carbon and hydrogen atoms are positioned so that they overlap to form a new, shared orbital lying directly between the bonded atoms.
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| σ-bonds are the strongest type of covalent bond. What makes them so strong? | The high electron density between the nuclei means there is a strong electrostatic attraction between the nuclei and the shared pair of electrons. This means that σ-bonds have a high bond enthalpy. |
| TRUE OR FALSE: Bonded atoms are free to rotate around the σ-bond | TRUE Whichever way the atoms point, the atomic orbitals between them will overlap |
| TRUE OR FALSE: Alkanes are very reactive | FALSE They are UNreactive |
| What types of reactions do alkanes undergo? | Combustion with oxygen Substitution reactions with highly reactive free radical species |
| Why do alkanes have a low reactivity? | The C-C and C-H σ-bonds all have a large bond enthalpy, making them very strong and difficult to break The bonds are non-polar - they won't attract any positively or negatively charged particles |
| What does the boiling point of an alkane depend on? | Size Shape |
| How does the size of an alkane affect the boiling point? | The longer the carbon chain, the more London forces there are. Longer carbon chains have a larger molecular surface area so there is more surface contact between the molecules and there are more electrons to interact |
| How does the shape of an alkane affect boiling point? | A branched alkane has a lower boiling point than its straight-chain isomer. Branched-chain alkanes can't pack closely together and they have smaller molecular surface areas - so the London forces are reduced |
| What are the two types of combustion? | Complete Incomplete |
| What are the products of complete combustion? | Carbon dioxide Water |
| Give the balanced symbol equation for the complete combustion of propane | C₃H₈ + 5O₂ --> 3CO₂ + 4H₂O |
| TRUE OR FALSE: Complete combustion reactions can happen with liquid alkanes | FALSE Complete combustion reactions happen between GASES, so liquid alkanes have to be vaporised first |
| TRUE OR FALSE Smaller alkanes turn into gases more easily | TRUE |
| What is the term used to describe a substance's ability to turn into a gas? | Volatility |
| Complete the sentence: Smaller alkanes are _______ volatile, so they'll burn ______ easily too | Smaller alkanes are MORE volatile, so they'll burn MORE easily too. |
| Alkanes make excellent fuels. Why? | When alkanes burn, some energy is used to break the covalent bonds but more energy is released by forming the new products. |
| Do larger alkanes or smaller alkalkanes release more energy per mole? | Larger alkanes (more CO₂ and H₂O are formed) |
| Alkanes make excellent fuels. What is the use of propane? | Central heating Cooking fuel |
| Alkanes make excellent fuels. What is the use of butane? | Bottled and sold as camping gas |
| What are petrol and diesel made up of? | A mixture of alkanes and additives |
| What are the products of incomplete combustion? | Carbon monoxide Water |
| Give the balanced symbol equation for the incomplete combustion of methane | 2CH₄ + 3O₂ --> 2CO + 4H₂O |
| Why would breathing in carbon monoxide be dangerous? | Carbon monoxide is better at binding to haemoglobin than oxygen is. This means that less oxygen will reach your cells |
| What are the symptoms associated with carbon monoxide poisoning? | Fatigue Headaches Nausea |
| Name 3 appliances that produce carbon monoxide | Gas- or oil-fired boilers and heaters Gas stoves Cool or wood fires Cars (Any appliance that burns alkanes can produce CO) |
| What could be done to prevent carbon monoxide poisoning? | All appliances that use an alkane-based fuel need to be properly ventilated, checked and maintained regularly Carbon moonoxide detectors should be used |
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