Question

Carbon dioxide, CO₂, changes from the solid phase to the gas phase at 1 atm and 194.5 K. In the solid phase, CO₂ is often called dry ice. When dry ice sublimes in air at 298 K, the water vapor in the air can condense, forming a fog of small water droplets. This fog is often used for special effects at concerts and in movie-making.
1. State the direction of heat flow between the dry ice and the water vapor in the air.
2. At 1 atm and 298 K, compare the potential energies of the water molecules before and after the water vapor condenses.
3. At 1 atm and 190. K, compare the amount of thermal energy in a 1.0-kilogram block of dry ice to the amount of thermal energy in a 2.0-kilogram block of dry ice.

Answer 1

Answer:

1. From water vapor to the dry ice;

2. The potential energy is higher before the water vapor condenses;

3. The thermal energy is higher in the 2.0 kg block.

Explanation:

1. The heat flows from the system with high temperature to the system with low temperature. The water vapor is at 298 K, and the dry ice is at 194.5 K.

2. The energy of the molecules is related to the temperature and the physics state. At the gas state, the molecules are more agitated, and the energy is higher than the liquid state. So, when the vapor condenses to a liquid, the energy decreases.

3. The thermal energy can be calculated by:

Q = m*c*ΔT

Where m is the mass, c is the specific heat, and ΔT the variation in the temperature. So, when the mass increase, thermal energy also increases.