Question

Homework: Name: 1. At the top of Mount Everest, water boils at 70 °C. Explain why this is lower than its usual boiling point of 100°C. 2. a) How much heat is needed to heat 33.9 g of acetone (C3H&0) from 25.0°C to its boiling point of 56.05°C? (Specific heat of acetone is 2.15 J/g.C) b) How much heat is required to vaporize 33.9 g of acetone at its boiling point? (AHvap for acetone is 29.1 kJ/mole) 3. How much heat does your body lose when 5.86 g of sweat evaporates from your skin (Assume that the sweat is only water.) AHvap for water is 44.0 kJ/mole. 4. Write the type of solid (Molecular, ionic, metallic, or covalent network solid) next to each solid and then arrange the solids from lowest to highest melting point a) C(s, diamond) b) Kr(s) c) NaCl(s) d) H2O(s)

Answer 1

Q1: When a liquid is heated, the liquid vapourises from the surface. The pressure exerted by vapours on the walls the container is called vapour pressure. The temperature at which vapour pressure of the liquid becomes equal the external pressure is called boiling temperature of the liquid at that external pressure. At high altitudes atmospheric pressure is low. For example, at sea level, the atmospheric pressure is 1 atr whereas at the summit of Mount Everest it is 0.329 atm. Hence at high altitudes, the liquid boils at a lower vapor pressure, thus at a lower temperature. For Q2 and Q3, you can use the equation, Q=m*C*dT where Q is the amount of heat transferred, C is heat capacity, dT is the change in temperature, m is mass of th substance. Take care of unit conversions!