Page 9 - Physical chemistry understanding our chemical world

viii CONTENTS

4.3 Introducing the Gibbs function 144
Why is burning hydrogen gas in air (to form liquid water) a spontaneous
reaction? 144
How does a reflux condenser work? 144
4.4 The effect of pressure on thermodynamic variables 148
How much energy is needed? 148
Why does a vacuum ‘suck’? 151
Why do we sneeze? 152
How does a laboratory water pump work? 153
4.5 Thermodynamics and the extent of reaction 156
Why is a ‘weak’ acid weak? 156
Why does the pH of the weak acid remain constant? 158
Why does the voltage of a battery decrease to zero? 159
Why does the concentration of product stop changing? 162
Why do chicken eggs have thinner shells in the summer? 165
4.6 The effect of temperature on thermodynamic variables 166
Why does egg white denature when cooked but remain liquid at room
temperature? 166
At what temperature will the egg start to denature? 170
Why does recrystallization work? 171

5 Phase equilibria 177
5.1 Energetic introduction to phase equilibria 177
Why does an ice cube melt in the mouth? 177
Why does water placed in a freezer become ice? 181
Why was Napoleon’s Russian campaign such a disaster? 182
5.2 Pressure and temperature changes with a single-component system:
qualitative discussion 184
How is the ‘Smoke’ in horror films made? 184
How does freeze-drying work? 185
How does a rotary evaporator work? 188
How is coffee decaffeinated? 189
5.3 Quantitative effects of pressure and temperature change for a
single-component system 192
Why is ice so slippery? 192
What is ‘black ice’? 193
Why does deflating the tyres on a car improve its road-holding on ice? 198
Why does a pressure cooker work? 199
5.4 Phase equilibria involving two-component systems: partition 205
Why does a fizzy drink lose its fizz and go flat? 205
How does a separating funnel work? 207
Why is an ice cube only misty at its centre? 208
How does recrystallization work? 209
Why are some eggshells brown and some white? 211