Read Chemistry
Definition of Matter and Energy
What is Matter?
– Matter is anything that has mass and occupies space.
– Mass is a measure of the quantity of matter in a sample of any material.
– The more massive an object is, the more force is required to put it in motion.
– All bodies consist of matter. Our senses of sight and touch usually tell us that an object occupies space.
– In the case of colorless, odorless, tasteless gases (such as air), our senses may fail us.
What is Energy?
– Energy is defined as the capacity to do work or to transfer heat.
– We are familiar with many forms of energy, including mechanical energy, light energy, electrical energy, and heat energy.
– Light energy from the sun is used by plants as they grow, electrical energy allows us to light a room by flicking a switch, and heat energy cooks our food and warms our homes.
– Energy can be classified into two principal types: kinetic energy and potential energy.
– A body in motion, such as a rolling boulder, possesses energy because of its motion. Such energy is called kinetic energy.
– Kinetic energy represents the capacity for doing work directly. It is easily transferred between objects.
– Potential energy is the energy an object possesses because of its position, condition, or composition.
– Coal, for example, possesses chemical energy, a form of potential energy, because of its composition.
– Many electrical generating plants burn coal, producing heat, which is converted to electrical energy.
– A boulder located atop a mountain possesses potential energy because of its height. It can roll down the mountainside and convert its potential energy into kinetic energy.
– We discuss energy because all chemical processes are accompanied by energy changes.
– As some processes occur, energy is released to the surroundings, usually as heat energy. We call such processes exothermic. Any combustion (burning) reaction is exothermic.
– Some chemical reactions and physical changes, however, are endothermic; that is, they absorb energy from their surroundings.
– An example of a physical change that is endothermic is the melting of ice.
The Law of Conservation of Matter
– When we burn a sample of metallic magnesium in the air, the magnesium combines with oxygen from the air (Figure 1) to form magnesium oxide, a white powder.
– This chemical reaction is accompanied by the release of large amounts of heat energy and light energy.
– When we weigh the product of the reaction, magnesium oxide, we find that it is heavier than the original piece of magnesium.
– The increase in the mass of a solid is due to the combination of oxygen from the air with magnesium to form magnesium oxide.
– Many experiments have shown that the mass of the magnesium oxide is exactly the sum of the masses of magnesium and oxygen that combined to form it.
– Similar statements can be made for all chemical reactions. These observations are summarized in the Law of Conservation of Matter: (in brief)
There is no observable change in the quantity of matter during a chemical reaction or during a physical change.
– This statement is an example of a scientific (natural) law, a general statement based on the observed behavior of matter to which no exceptions are known.
– A nuclear reaction is not a chemical reaction.
The Law of Conservation of Energy
– In exothermic chemical reactions, chemical energy is usually converted into heat energy. Some exothermic processes involve other kinds of energy changes.
– For example, some liberate light energy without heat, and others produce electrical energy without heat or light.
– In endothermic reactions, heat energy, light energy, or electrical energy is converted into chemical energy.
– Although chemical changes always involve energy changes, some energy transformations do not involve chemical changes at all.
– For example, heat energy may be converted into electrical energy or into mechanical energy without any simultaneous chemical changes.
– Many experiments have demonstrated that all of the energy involved in any chemical or physical change appears in some form after the change.
– These observations are summarized in the Law of Conservation of Energy: (in brief)
Energy cannot be created or destroyed in a chemical reaction or in a physical change. It can only be converted from one form to another.
The Law of Conservation of Matter and Energy
– With the dawn of the nuclear age in the 1940s, scientists, and then the world, became aware that matter can be converted into energy.
– In nuclear reactions, matter is transformed into energy.
– The relationship between matter and energy is given by Albert Einstein’s now famous equation
E = mc2
– This equation tells us that the amount of energy released when matter is transformed into energy is the product of the mass of matter transformed and the speed of light squared.
– At the present time, we have not (knowingly) observed the transformation of energy into matter on a large scale. It does, however, happen on an extremely small scale in “atom smashers,” or particle accelerators, used to induce nuclear reactions.
– Now that the equivalence of matter and energy is recognized, the Law of Conservation of Matter and Energy can be stated in a single sentence: (in brief)
The combined amount of matter and energy in the universe is fixed.
References:
- Principles of Inorganic Chemistry / Brian W. Pfennig / 1st ed, 2015 /John Wiley & Sons, Inc/ USA.
- Inorganic Chemistry /Peter Atkins, Tina Overton, Jonathan Rourkel, Mark Weller, Fraser Armstrong, Mike Hagerman / 6th ed, 2014 /W. H. Freeman and Company/ New York, USA.
-
