Intermolecular forces and physical propertiesEdexcel International A Level Chemistry: Flashcards

What these 13 flashcards ask

What is overcome when a molecular liquid boils?
What does 'volatile' mean?
Which forces act between alkane molecules?
Why does the boiling temperature of alkanes rise with chain length?
Why does branching lower the boiling temperature of an alkane?
Which has the higher boiling temperature, pentane or 2,2-dimethylpropane?
Why do isomers have the same number of electrons?
Why is methanol much less volatile than ethane?
Why must you state the number of electrons when comparing an alcohol with an alkane?
Why does the boiling temperature of the alcohols rise with chain length?
What explains the rise in boiling temperature from HCl to HI?
Why does HF have a higher boiling temperature than HCl?
Why is HF out of line with the trend in boiling temperatures?

Exam questions on Intermolecular forces and physical properties

Alkanes are used as fuels. The boiling temperatures of the first four straight-chain alkanes are: methane 112 K, ethane 184 K, propane 231 K and butane 273 K.
Predict whether the boiling temperature of pentane is higher or lower than that of butane. Give a reason.2 marks
Pentane, 2-methylbutane and 2,2-dimethylpropane are isomers with the molecular formula C₅H₁₂. Pentane has an unbranched chain, 2-methylbutane has one methyl branch and 2,2-dimethylpropane has two methyl branches on the same carbon atom. Their boiling temperatures are 309 K, 301 K and 283 K respectively.
Explain why pentane has a higher boiling temperature than 2-methylbutane.2 marks
Methanol, CH₃OH, and ethane, C₂H₆, each have 18 electrons per molecule. Methanol boils at 338 K and ethane boils at 184 K. Propan-1-ol, CH₃CH₂CH₂OH, and butane, C₄H₁₀, each have 34 electrons per molecule, and ethanol, C₂H₅OH, has 26 electrons per molecule.
Explain why methanol has a much higher boiling temperature than ethane.3 marks

Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).