CHEM 121 Lecture Notes - Lecture 35: Ethylene Glycol, Diethyl Ether, Vapor Pressure
6 Aug 2015
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Chem121 - lecture 35 - changes of state and properties of solutions. Temperature remains constant during a phase change. Specific heat of a substance is the energy required to raise the temperature of 1g of a substance by 1 degree. Heating vapour (specific heat of vapour in j/goc) Step 1: cool vapour from 110oc to bp q1 = 324g x specific heat of vapour x t q1 = 324g x (2. 08 j/goc) x (100-110)oc (exothermic) Step 2: condense to liquid at bp q2 = 324g x enthalpy of condensation q2 = 324g x (-2258 j/g) (exothermic) Step 3: cool liquid from bp to 45oc q3 = 324g x specific heat of liquid x t q3 = 324g x (4. 18 j/goc) x (45-100)oc (exothermic) Total heat is sum of these 3 steps. Boiling: evaporation that occurs within the body of a liquid through bubble formation. Boiling point: temperature at which the vapour pressure is equal to the external (atmospheric) pressure.
