Some of the most useful and powerful properties of matter are those related to how and why matter changes. There are countless changes in matter that affect us every day: for example, freezing water, baking a cake, and lighting a sparkler. Understanding and categorizing the kinds of changes we see in matter are an important first step in making use of matter.
Earlier we looked at the physical and chemical properties of matter. Some of the most useful and powerful properties of matter are those related to how and why matter changes. In our daily lives, there are many examples of how understanding and controlling changes in matter help us meet our basic needs.
You can discover a great deal about matter simply by observing a candle. The candle undergoes both physical and chemical changes. Which change result in new substances? Which does not?
Changed, Yet Still There
While the physical property of substance describes a characteristic of a substance that can be observed or measured, a physical change occurs when a material changes its size or shape but still remains the same material. The physical properties of a candle include its colour, texture and density – properties that do not affect the ability of the wax to change in any way.
Some other physical properties do change wax. For example, the wax melts at a definite temperature called the melting point and then changes to vapour at a temperature called the boiling point. The solid (wax) becomes liquid and the liquid becomes solid again when cooled. These physical properties affect the ability of wax to undergo physical change – the wax, whether solid, liquid, or vapour, is still the same substance.
As the candle burns, you can observe another kind of property that affect change in the wax – combustibility. Candle wax burns, producing light and heat. Combustibility is a chemical property that describes the ability of the wax to react with oxygen to produce new substances.
Unlike physical properties, chemical properties always involve change in a substance. In the candle, the wax becomes carbon dioxide, water and energy. As the wax in the candle melts and vaporizes, some wax particles join up with oxygen from the air. The result of this chemical change is the production of water vapour, carbon dioxide gas, heat, and light. The wax particles that seem to disappear are actually changing into something else.
Chemical changes always involve the production of new substances with different properties from the original. Whenever a chemical change occurs, the chemical properties are revealed. You may not see the chemical change in the wax just by looking at the burning candle, but you can tell that it occurred due to the heat and light that is given off.
Chemical changes are permanent and difficult to reverse. Burning, cooking, and rusting are all other examples of chemical changes.
Physical Change and the Environment
In our environment there is evidence of physical changes in our weather. Change of state – melting, boiling, freezing, condensation, sublimation – are physical changes evident in our weather.
Evaporation is the changing of liquid water to invisible water vapor. Condensation is the reverse process. Sublimation is the changing of ice directly to water vapor, or water vapor to ice, bypassing the liquid state in each process. Condensation or sublimation results in cloud formation and snow or ice crystals result from the sublimation of water vapor directly to the solid state.
When you dissolve salt in water, it is a physical change. The salt particles spread out, but they are still there, as salt particles. You can reverse the process by evaporating the salt and collecting the salt. The ocean is the largest body of salt dissolved in water. You can boil or evaporate the water and the salt will be left behind as a solid. If you want to collect the water, you can use distillation.
You see physical change when you pour melted chocolate over ice cream. Liquid chocolate forms a thin, even coating over the ice cream. The chocolate becomes solid as the ice cream cools it, but once it’s in your mouth, it tastes the same in both states because its particles have not changed.
Signs of Chemical Change Around Us
Evidence of chemical change can be seen in the kitchen. Heating can result in chemical changes when baking a cake. baking soda is heated, it undergoes a chemical change that results in the production of carbon dioxide gas. It is this gas that lifts the cake and make it light and fluffy. If you forget to add baking soda to a cake batter, the cake will be flat and dense.
Combustibility – the ability of a substance to react quickly with oxygen when a flame is applied, to produce heat energy and light, is a chemical property of wood. The heat energy produces a chemical change and carbon dioxide, water vapour and carbon are produced. The wood is reduced to ashes, an irreversible process.
A chemical change can take when some substances are mixed. For example, an ice pack or cold pack is used to help relieve pain and swelling or cool a fever when it absorbs heat from the surroundings. When you break the tube inside so that the water mixes with the non-toxic chemical, a chemical change occurs and the pack feels cold to the touch.
Fireworks designers know that when certain substances are heated they will combine explosively to form new substances. When fireworks explode, gases form from the solids in the fireworks. They also know that certain substances will change colour when they are heated, therefore adding these types of substances to fireworks creates the spectacular fireworks we observe in the night sky.
Changes in Matter and Indigenous Traditions
First Nations people of Canada understood details about the properties of matter without knowing the scientific ideas of physical and chemical changes. Their ideas about the physical world served them very well. Their way of knowing and the scientific way do not contradict each other. Both add to humanity’s understanding.
Preservation of Fish. Understanding matter and it many transformations allowed First Nations people to prevent spoilage and allowed them to store meat which would otherwise quickly rot in the heat of summer. The skills of preserving fish allowed First Nations people to store their catch in the summer for eating in the winter.
Whitefish, jack fish and red sucker fish made up a large part of their diet. To preserve these fish, the smoked them. First the scales were removed and the fish prepared. A lean-to made out of wood with a fire lit under it made from old dried poplar wood produced the best smoke. Often it takes two days for the fish to be completely smoked and ready to eat. This process of dehydration slows down decomposition by bacteria, and it ensured that the First Nations people could preserve their catch for a few days in the summer or for eating during the winter.
Painting. Rock painting created by First Nations people along the Churchill River in northern Saskatchewan are believed to be hundreds of years old. They used ochre, a reddish-brown mineral, to give colour to their paint.
Ingeniously, these people also know how to stop their paintings from fading over time due to exposure from water and the sun. They made a gelatin-like substance, called “isinglass”, from dried swim bladders of freshwater fish and mixed it with ochre to add to the paint.
Controlling Changes to Matter
There are many examples of how understanding and controlling changes in matter help us to meet our basic needs in our daily lives. Being able to change materials from one form to another allows us to make products that are not only useful but also support a sustainable environment.
One example is the use of corn to produce chemicals. Corn can be put through a chemical change called fermentation to produce new substances such as biodegradable plastics and automobile fuel. An advantage of corn-based biodegradable plastics is that they can be broken down by bacteria.
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