Problem 4 - Chemistry

Question

Heat is applied to an ice cube in a closed container until only steam is present. Draw a representation of this process, assuming you can see it at an extremely high level of magnification. What happens to the size of the molecules? What happens to the total mass of the sample?

Step-by-Step Solution

Answer

During the process of transforming an ice cube to steam, the water molecules undergo two phase changes: melting and boiling. Their size remains unchanged, but their arrangement changes due to broken hydrogen bonds. Initially, they're in an ordered lattice structure (ice). When melting occurs, water molecules become less ordered and free. In the boiling stage, the molecules are further apart and move freely (steam). The total mass of the sample remains constant but the volume increases significantly as the distance between molecules increases during these phase changes.

Step 1: Understand the phase change from ice to steam

First, it is important to know that when heat is added to an ice cube, it will undergo two phase changes: from ice to water (melting) and from water to steam (boiling). The energy absorbed during these changes will break the bonds between molecules, allowing them to move more freely.

Step 2: Represent the starting state (ice)

In the initial state, the ice cube consists of water molecules arranged in an orderly lattice structure, with strong hydrogen bonds between them. Draw a group of water molecules (H2O) in a hexagonal lattice formation, representing the bond between molecules with dashed lines. Indicate the presence of ice using a label.

Step 3: Represent the melting process (ice to water)

As heat is added, the hydrogen bonds between the water molecules are broken and they start to move more freely. Represent this by showing some of the water molecules moving apart from the lattice formation, and some of the dashed lines between molecules disappearing. Water molecules are still close to each other and no observable increase in size occurs. Label this stage as "melting".

Step 4: Represent the boiling process (water to steam)

As more heat is added, the water molecules gain enough energy to break free from remaining bonds and become steam. Represent this by drawing water molecules that are further apart from each other and moving freely. There will be no bonds between the molecules. The water molecules themselves do not change in size, but the space between them increases substantially. Label this stage as "boiling".

Step 5: Describe the changes during the phase transition

As the phase transition occurs from ice to steam, the size of the water molecules does not change. However, the total volume of the sample increases significantly, as the distance between the molecules increases. The total mass of the system remains constant, as no molecules are gained or lost, only the form in which they reside changes.