Day 53 MCAT Practice Question

Passage 9: Thermodynamics

In a series of experiments that investigated the thermodynamics of phase changes,

the journey of a water molecule as it transitions from ice to steam and back to

liquid water was documented. It began with a block of ice at -10°C, which was

gradually heated with a controlled heat source. The ice melted, boiled into steam,

and finally condensed back into water. Temperature changes were meticulously

recorded, and heat input at each stage was determined via sensors on the heat

source.

The previous results applied to an open system (the water was open to the

atmosphere). The team also monitored how energy input values changed when a

closed system was used instead. They found that the amount of energy required

to boil the water was dramatically affected by this adjustment, but not the energy

required to melt the ice.

Which of the following statements about the experiment in the passage is an

assumption related to the first law of thermodynamics?

A) The total energy absorbed during melting and boiling must be equal to the

energy released during condensation and freezing

B) Temperature of the ice block increases linearly with heat input during the

initial warming phase

C) The entropy change for water entering the gas phase is greater than the

entropy change for ice entering the liquid phase

D) The heat capacity of water remains constant across all phases