Explaining Matter: Chemical Change (1960)

[Applause] chemical change is a particular kind of change in chemical changes two or more kinds of material combine with each other to produce entirely different materials a chemistry laboratory is not the only place where you can see chemical changes taking place in fact the most common and important chemical changes are going on all around you burning is a common chemical change the wood changes into different materials smoke Steam and Ashes the growth of plants depends upon chemical changes air water and soil combine to produce roots and leaves chemical changes inside your digestive system change the food you eat into the materials that build your body in fact all life is dependent upon many complex chemical changes in order to understand what a chemical change is we have to understand what materials are made of water is a common material let's see what it's made of if we could look at it closely enough even more closely than we can see with the most powerful microscopes we would see that water like all materials is made up of small particles called molecules if we could look still more closely we would see that each molecule is made up of still smaller particles called atoms every material in the world is made up of its own kind of molecules each molecule in turn is made up of certain kinds of atoms now let's see what happens to atoms and molecules when a chemical change takes place this material is called mercuric chloride a mercuric chloride molecule is made up of one atom of mercury and two atoms of chlorine this other material is pottassium iodide a potassium iodide molecule is made up of one atom of iodine and one atom of pottassium which is a type of metal now we'll dissolve the mercuric chloride and the potassium iodide in water when the two solutions are mixed together a chemical change takes place and new materials are formed this mixture has changed color because it contains a new material which is orange colored this material is called mercuric iodide its molecule is made up of one atom of mercury and two atoms of iodine when we mix the two materials together iodine from the potassium iodide molecules replaced the chlorine of the mercuric chloride molecules forming molecules of mercuric iodide a chemical change takes place when atoms from the molecules of two or more materials join with each other to form molecules of entirely different materials let's watch that again iodine from the potassium iodide replaces the chlorine of the mercuric chloride leaving molecules of an entirely different material mercuric iodide here's another chemical change when a piece of wood burns many of the molecules that make up the wood combine with oxygen molecules from the surrounding air to produce molecules which form new materials that are neither oxygen nor wood we can't see the oxygen that's used in this chemical change because it's a colorless gas but if the supply of oxygen were cut off the burning would stop this jar cuts off the supply of oxygen from the candle flame when there are no longer enough oxygen molecules left inside the jar to continue combining in a chemical change with molecules from the candle the flame goes out fire is one of many chemical changes which produce energy a fire gives off energy in the form of light and [Applause] heat here's another kind of energy also the result of chemical changes chemical changes inside your body combine the food you eat with the oxygen you breathe to produce energy when you need extra energy you breathe harder in order to get more oxygen molecules into your body to be used in these chemical [Music] changes when you exhale you breathe out a gas called carbon dioxide dioxide plays a vital part in one of the most important of all chemical changes this chemical change takes place in the green leaves of growing plants but but only when energy is present in the form of sunlight the materials involved in this change are water and carbon dioxide which is always present in the air much of it the result of the breathing of man this is a model of a molecule of carbon dioxide it contains one carbon atom and two oxygen atoms you remember that a molecule of water has two hydrogen atoms and one oxygen atom water enters a plant through its roots and the water molecules are stored in the leaves molecules of carbon dioxide pass into the leaves from the air inside the leaf in the presence of the green coloring matter called chlorophyll and with energy from the sunlight a chemical change takes place six molecules of water and six molecules of carbon dioxide combine with each other to produce a molecule which contains six carbon atoms 12 hydrogen atoms and six oxygen atoms this is a molecule of Sugar by this chemical change which is called photosynthesis plants produce food the plants use this food to grow and we use it too when the sugar molecule is produced there are 12 oxygen atoms left over they form six molecules of oxygen these molecules are not wasted if we look at a plant growing underwater we can see bubbles they are caused by the oxygen passing from the leaves back into the air once in the air the oxygen can be breathed again in a chemical change the atoms from the molecules of two or more kinds of materials combin to produce molecules of entirely different materials many chemical changes give off [Applause] energy outside source of energy is the sun in order to take place new materials are formed but no material is chemical changes wherever there is life chemical changes are taking place B