Explain the following observations by reference to the type of bonding present and/or the forces between organic molecules: The compounds ethanol (CH3CH2OH) and formic acid (HCOOH) have molecular masses of 46 gmol-1 but different boiling points: Compound Boiling point   Ethanol 78.5 °C Formic acid 100.8 °C

Based on the thermodynamic properties provided for water, determine the amount of energy needed for 2.20 kg of water to go from -14.0 °C to 74.0 °C. 6.50 Property Melting point Boiling point AHfus AHvap Cp (s) Cp (1) Cp (g) kJ Value 0.0 100.0 6.01 40.67 37.1 75.3 33.6 Units °C °℃ kJ/mol kJ/mol J/mol • °C J/mol • °C J/mol • °C

Compare the boiling points of the various isomeric hydrocarbons shown in the table below. Notice the relationship between boiling point and structure; branched-chain hydrocarbons have lower boiling points than the unbranched isomer. Speculate on possible reasons for this trend. Why might the intermolecular forces be slightly different in these compounds? Compound Boiling Point (°C) 68.9 Hexane 3-Methylpentane 2-Methylpentane 2,3- Dimethylbutane 2,2- Dimethylbutane 63.2 60.3 58.0 49.7 The more branched structure has smaller exposed surface and hence weaker dispersion intermolecular forces. The more branched structure has larger exposed surface and hence weaker dispersion intermolecular forces. The more branched structure has larger exposed surface and hence stronger dispersion intermolecular forces. The more branched structure has smaller exposed surface and hence stronger dispersion intermolecular forces.

273.15 K = 0 °C NA = 6.02, RT/F = 0.025693 V (RT/F) In10 = 0.059160 V @ T = 298.15 K R = 8.3145 J K-1 mol-¹ = 0.082057 L atm K-1 mol-1 F = 96,485.3 C/mol 1 atm = 1.01325 bar = 760 Torr = 101325 Pa 1023 mol-1