At this level, it is sufficient to qualitatively compare the diffusion rates of liquids and gases. We will not make a controlled quantitative comparison of diffusion rates. It would be possible to convert the study into a controlled experiment by using identical containers to compare diffusion rates and comparing gases and liquids with particles of similar size. It would then also be necessary to choose a colored gas (e.B brominated gas) so that learners can see the diffusion process in the container as it progresses. It is important to note that bromine is a dangerous gas and is not available for free. It would only be advisable to use this example if you have the facilities and training to work safely with bromine. An alternative substance that effectively demonstrates gas diffusion is hydrogen sulfide (H2S). A few drops of hydrochloric acid on iron sulfide or sodium sulfide in an Erlenmeyer flask produce H2S. This can be used instead of vanilla essence. It is important to note that H2S has a very strong and pungent smell (characteristic smell of rotten eggs).
It is not toxic at low concentrations, but it is important to make sure that the room is well ventilated and the windows are open. It may not be ideal to use H2S as an example if the classroom is very small or crowded. You can also light a “smoke bomb” (available in toy stores) outside the classroom if allowed in your school. Mixing smoke with air is an effective analogy with gas mixing, although smoke actually contains fine solid soot particles and is not necessarily a gas. 2.7 The expansion and contraction of materials (2 hours) (figure) lists representative values of the linear expansion coefficient, which can have units of or 1/K. Since the size of a Kelvin and a degree Celsius is the same, both can be expressed in units of Kelvin or degrees Celsius. The equation is accurate for small temperature changes and can be used for large temperature changes if an average value of is used. The thermal expansion and contraction of concrete varies mainly depending on the type of aggregates (shale, limestone, gravel, granite), cementitious material content, water-to-cement ratio, temperature range, concrete age and relative humidity. Among these factors, the type of aggregate has the greatest influence on the expansion and contraction of concrete.
where the coefficient of volume expansion is and. Heat stress occurs when heat expansion is limited. Liquids and solids expand as the temperature increases because the kinetic energy of atoms and molecules in a body increases. Explain why some materials shrink as the temperature rises. Perform this calculation on the board. Learners must be able to exchange between units. 1000 x 1000 = 1,000,000 milligrams in one kilogram. You can also do other examples, for example. B ask how many grams in 1.25 kg (1250 g), how many milligrams in 12.5 grams (12,500 mg)? Let`s look at a thermometer to understand expansion and contraction. Use the linear thermal expansion equation to calculate the length change. Use the linear expansion coefficient , for the steel of (figure), and note that the temperature change is , ,.
The expansion of alcohol in a thermometer is one of many common examples of thermal expansion, changing the size or volume of a particular mass with temperature. Hot air increases because its volume increases, which causes the density of warm air to be lower than the density of the surrounding air, resulting in a floating force (upwards) on the hot air. The same happens in all liquids and gases, resulting in a transfer of natural heat into homes, oceans and weather systems. Solids are also subject to thermal expansion. Railway rails and bridges, for example, have expansion joints so they can expand and contract freely when the temperature changes. Ask learners to discuss this question. They learned that particles move faster at higher temperatures. How would this affect the distances between the particles? Most solids and liquids tend to become less dense when they heat up.
Learners do not have to draw any conclusions at this stage. However, the question will help to introduce the concepts of contraction and expansion. If you have trouble finding objects of the same size, you can start with containers that have the same volume and fill them with different substances. For example, you can use matchboxes (all of which have the same volume) and fill them with various substances such as sand, flour, sugar, cotton, etc. In the following diagram, the image on the left shows a concrete path or road surface. How did the engineers who built the road allow an extension? This activity is used to explain the general property that solids are denser than liquids that are denser than gases. It is mentioned that the boxes contain the “same material”, which is important. Water is explicitly not mentioned in this activity, as it is an exception that will be discussed later. Water does not behave like other materials because the solid phase is actually less dense than the liquid phase in water. .