Question

phases.

a. in which phase(s) do molecules move freely?

b. in which phase(s) are molecules held together?

c. what do you notice about the positions of the ice molecules?

1. click reset ( ), and select macro view. set the ice volume to 25 cm³.

a. in which phase(s) is water held in a defined shape?

b. in which phase(s) does the water take the shape of the container?

activity a:
phase changes

get the gizmo ready:

• click reset. check that macro view is selected.
• set the water temperature to 10 °c.
• set the ice volume to 0 cm³.

question: how is temperature related to phase changes?

1. predict: based on your prior knowledge, predict the following:

Explanation:

1. Predictions (Question 1)

A. In which phase(s) do molecules move freely?

In the gas phase, molecules have high kinetic energy, move freely, and are far apart. In the liquid phase, molecules can also move more freely than in solids (they can slide past each other). So gas and liquid phases (or "liquid and gas" or "gas, liquid" – also, sometimes liquid is considered to have molecules that can move but with more intermolecular forces than gas; solid molecules vibrate in place and don't move freely). So the answer is gas (and sometimes liquid, but gas is the primary where they move most freely; if considering both, liquid and gas). But typically, gas phase molecules move freely (liquid has some movement but less than gas; solid is fixed). So for "move freely" – gas (and liquid, as liquid molecules can move around within the liquid, unlike solids which are fixed in a lattice). So the phases are liquid and gas (or gas and liquid).

In solid, liquid, and gas phases, molecules are held together by intermolecular forces (though in gas, the forces are very weak). But solids have strong intermolecular forces holding molecules in a fixed lattice. Liquids have moderate forces holding them together (molecules are close). Gases have weak forces but still some attraction. However, the question is "held together" – so all three? But more strongly in solid and liquid. Typically, solid and liquid phases have molecules held together (in solid, rigidly; in liquid, less rigidly). Gas molecules are far apart but still have some intermolecular forces (though very weak). But the main phases where molecules are held together (with significant intermolecular forces) are solid and liquid. So the answer is solid and liquid (and gas, but less so). But usually, solid and liquid.

Ice is a solid (water in solid phase). In a solid, molecules (like water molecules in ice) are arranged in a regular, repeating lattice structure (crystalline structure). They are fixed in position (vibrate in place but don't move around freely) and are closely packed in an ordered arrangement (due to hydrogen bonding in ice, forming a hexagonal lattice, for example). So the positions of ice molecules are fixed in a regular, ordered (crystalline) structure; they are arranged in a repeating pattern and don't move freely (just vibrate).

Answer:

Liquid and Gas (or Gas and Liquid; also, sometimes just Gas is considered, but liquid molecules do move more freely than solids)

B. In which phase(s) are molecules held together?