Equal amounts (in moles) of ethanol (CH₃CH₂OH) and hexane (C₆H₁₄) are each mixed with…
CHEMISTRY · Single correct · A Level · Chemistry · Bonding · Bonding
Problem
Equal amounts (in moles) of ethanol (CH₃CH₂OH) and hexane (C₆H₁₄) are each mixed with water at 25 °C. The ethanol–water mixture warms slightly, whereas the hexane–water mixture cools slightly. Which option best accounts for these observations?
(a) Ethanol is non-polar, so its dissolution is driven entirely by entropy and releases heat; hexane is polar, so its dissolution requires energy to overcome dipole–dipole forces.
(b) Ethanol forms strong hydrogen bonds with water, releasing more energy than is required to disrupt the original interactions; hexane cannot form hydrogen bonds with water, so its dissolution requires more energy than is released.
(c) Ethanol’s dissolution is endothermic because hydrogen bonds are broken, whereas hexane’s dissolution is exothermic because London dispersion forces are formed with water.
(d) Because ethanol has a lower molar mass than hexane, dissolving ethanol releases more kinetic energy, while hexane’s higher molar mass causes it to absorb heat from the surroundings.