Resources: Mini whiteboards, the presentation and the handout. Stearic acid, boiling tubes, thermometers, beakers, bunsen burner, tripod, gauze, heat proof mats. (Note: A class set of stearic acid in boiling tubes could be heated up in one beaker at the start of the lesson so the first four steps of the practical could be omitted).
Support Handout: Page 1; a changes of state diagram for the students to complete.
Core Handout: A flow chart for the students to complete with a challenge task included. Practical instructions and a ready drawn graph with axes, a scale and labels for some students to use to plot their graphs are included.
The students should be able to identify the three states of matter - solid, liquid and gas - and understand the characteristics of each state. They should also have a basic understanding of heat energy and its role in causing changes of state.
Ask the students: How many changes of state can you name? Ask them to list these on a mini whiteboard or create a mindmap in their books to show the transitions they know of.
Use the presentation slides to discuss what happens to the particles when a substance changes state. The first page of the handout provides a summary for students to label changes of state. Then, the students should explain their understanding of what happens to the particles when a substance undergoes a change of state. The students can then carry out a practical investigating the temperature as stearic acid changes state from a liquid to a solid.
Career Film: Take a tour around the offices of the Nuclear Decommissioning Agency (NDA) in Cumbria to find out about Melanie Brownridge's job. Melanie works as a Technology and Innovation Director for NDA.
Expert Film: This is Melanie Brownridge. Melanie works as a Technology and Innovation Director for the Nuclear Decommissioning Authority. Listen to Melanie as he explains the changes of state using the particle model.
Ask the students to complete the handout. This requires them to draw the arrangement of particles in each of the 3 main states of matter. They should then label each arrow with the correct name for the transition. In each box, above or below an arrow, the students should describe how the arrangement and movement of the particles change. This is explained to them during the presentation.
The students will then carry out an investigation into the temperature as liquid stearic acid cools and turns into a solid. They can plot a graph of their results and determine stearic acid’s melting/freezing point.
Support: A sheet to label the changes of state and a second support sheet for the practical that has a graph with scaled axes ready for results to be plotted.
Challenge: Ask the students to use particle models to explain their observations during transitions and why the physical properties of the material changes.
Discuss the results from the experiment and how could they could be used to determine the freezing point of stearic acid. (Note: it is likely that the stearic acid is impure and so may not get a horizontal line at the freezing point; this could be included in the discussion).
The famous particle model is used to explain the changes of state in terms of the properties of solids, liquids and gases. It explains how all matter is made up of particles and how these particles are attracted to one another and are constantly moving. In short, solids have a constant volume and a fixed shape, liquids have a constant volume but a variable shape and gases have a variable volume and shape. Let’s explore this.
The particles in a solid are usually arranged in a very regular way and are close together in nature. They are linked to one another via chemical bonds and are thus kept near one another. They vibrate in a fixed position and cannot move from place to place because the particles have a fixed shape and cannot move. They are very much fixed and cannot be compressed because there is no space to move and they are very close together.
Liquid particles are very different. They are close together and are arranged in a very random way. Because of this random arrangement, they can move around each other. They are still held together by bonds but these bonds are much weaker than those in the solid. This allows them to move around one another. Liquid particles cannot be compressed because again, they are too close to one another and have no space to move. However, they can move around each other which means that they flow and tend to take the shape of the bottom of their container. Think about bottles of water! The water will take the shape of the bottle or whichever container it is in.
Gas particles are different too. They are far apart from one another but like liquids, arranged in a random way too. They are very much randomly arranged which means that they can move in all different directions. Unlike solids and liquids, gases are not held together by bonds. This explains why they are pretty free to move around. Because they aren’t held together by bonds, they have space to move and thus can be compressed. They tend to fill the container in which they are placed too. They move very quickly but cannot escape when they are enclosed. They continue to bump into each other and the walls of their container. This increases the pressure in the container. Gas pressure is increased by an increase in temperature too.