what happens to matter when it is heated
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Particle Theory
Topics covered
Melting
Evaporating
Humid
Changes of land
The kinetic theory of matter can be used to explicate how solids, liquids and gases are interchangeable as a result of increment or decrease in heat energy. When an object is heated the move of the particles increases equally the particles get more energetic. If it is cooled the motion of the particles decreases as they lose energy.
Melting
In a solid the stiff attractions between the particles hold them tightly packed together. Even though they are vibrating this is not enough to disrupt the structure. When a solid is heated the particles gain energy and get-go to vibrate faster and faster. Initially the structure is gradually weakened which has the result of expanding the solid. Farther heating provides more energy until the particles start to interruption gratis of the structure. Although the particles are nonetheless loosely connected they are able to motility around. At this betoken the solid is melting to form a liquid. The particles in the liquid are the same as in the solid simply they have more energy. To cook a solid energy is required to overcome the attractions between the particles and allow them to pull them apart. The energy is provided when the solid is heated upwardly. The temperature at which something melts is called its "melting point" or melting temperature. At room temperature a material is a solid, liquid or gas depending on its melting temperature. Anything with a melting temperature higher than about 20oC is likely to be a solid under normal conditions. Materials have widely differing melting temperatures e.g. mercury -39oC, ice 0oC, salt 1081oC, aluminium 660oC and steel 1535oC. Everyday materials such as ice, butter and wax have unlike melting temperatures and can be used as examples with children.
Ice is probably the melting substance near children are familiar with. It can be problematic when trying to develop an understanding of melting as it does oftentimes appear to them to melt without any source of rut. Ice melts at room temperature because the surrounding air is warmer than the water ice and at a temperature above the melting temperature. The heat energy required to cook the ice comes from the surrounding air which will consequently become a little cooler.
Not all solids melt when they are heated. Some may undergo chemic changes as a result of heating. For case paper burns rather than melts.
Evaporating
Within a liquid some particles have more energy than other. These "more than energetic particles" may have sufficient energy to escape from the surface of the liquid as gas or vapour. This process is chosen evaporation and the result of evaporation is usually observed when puddles or clothes dry. Evaporation takes place at room temperature which is often well below the boiling point of the liquid. Evaporation happens from the surface of the liquid. As the temperature increases the rate of evaporation increases. Evaporation is also assisted by windy weather which help to remove the vapour particles from the liquid then that more escape.
Evaporation is a complex idea for children for a number of reasons. The process involves the apparent disappearance of a liquid which makes the procedure difficult for them to empathize. It is non easy to meet the h2o particles in the air. Also, evaporation occurs in a number of quite differing situations - such as from a puddle or basin of h2o where the amount of liquid obviously changes, to situations where the liquid is less obvious - such as clothes drying or even those where there is no obvious liquid at all to start with - such as bread drying out. A farther complication is that evaporation may be of a solvent from a solution e.g. water evaporating from salt water to leave salt. These situations are quite different yet all involve evaporation.
Evaporation may also involve liquids other than water e.g. perfume, petrol, air fresheners. The particle model can exist used to explain how it is possible to detect smells some distance abroad from the source.
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Boiling
If a liquid is heated the particles are given more than energy and move faster and faster expanding the liquid. The most energetic particles at the surface escape from the surface of the liquid every bit a vapour as information technology gets warmer. Liquids evaporate faster as they heat up and more than particles have plenty energy to break away. The particles demand free energy to overcome the attractions between them. As the liquid gets warmer more particles have sufficient free energy to escape from the liquid. Eventually even particles in the centre of the liquid course bubbles of gas in the liquid. At this signal the liquid is boiling and turning to gas. The particles in the gas are the aforementioned equally they were in the liquid they just have more free energy. At normal atmospheric pressure all materials have a specific temperature at which boiling occurs. This is called the "boiling point" or boiling temperature. As with the melting point the boiling betoken of materials vary widely eastward.g. nitrogen -210oC, alcohol 78oC, aluminium 459oC.
Any cloth with a boiling temperature below 20oC is likely to be a gas at room temperature. When liquids boil the particles must accept sufficient free energy to break abroad from the liquid and to diffuse through the surrounding air particles. As these particles cool downwardly and lose free energy they will condense and plow back to liquid. When steam is formed by h2o boiling at 100oC the particles quickly condense as the surrounding air temperature is probable to be much less that 100oC and then the particles cool rapidly. In fact the "steam" coming out of a boiling kettle tin can merely be seen because some of the gas particles take condensed to grade pocket-sized droplets of water.
When a gas turns to a liquid (condenses) or a liquid turns to a solid (solidifies) the particles lose free energy to the surround.
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Website maintainer: R. Jones Updated: November thirteen, 2000
Source: https://www.le.ac.uk/se/centres/sci/selfstudy/particle02.html
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