Each increase in pressure of 100 atm decreases the melting
point of ice by about 1.0°C.
(a) Estimate the temperature at which liquid water freezes
under a pressure of 400 atm.
(b) One possible explanation of why a skate moves
smoothly over ice is that the pressure exerted by the
skater on the ice lowers its freezing point and causes it
to melt. The pressure exerted by an object is the force
(its mass × the acceleration of gravity, 9.8 m s22) divided
by the area of contact. Calculate the change in freezing
point of ice when a skater with a mass of 75 kg stands
on a blade of area 8.0 × 1025 m2 in contact with the ice.
Is this sufficient to explain the ease of skating at a temperature
of, for example, 25°C (23°F)?
69. (a) Sketch the phase diagram of temperature versus