Energy and States of Matter sample essay
Everything changes, that is a fact. We can find changes, even in simple things that we use. Have you ever asked why does an ice cube turn back onto water when you let it stand outside the freezer? Or do you know why an ice cream melts? We knew about the three basic phases of matter – solid, liquid and gas. From our basic chemistry, we taught about the change of state or phase of matter wherein soli becomes liquid and liquid turns to gas and vice versa. The question is, why do they change phase?
To really understand those phenomena, we should look onto the two different graphical illustrations of the changes of states of a substance, cooling curve and heating curve and thereby understand what is really happening on the molecular structure of a substance. Heat is very crucial in these changes on the form of certain substances. This is the energy transformed between two objects brought about by the difference on both temperatures. It means, when you let an ice cube in a plate, after a day, you will find it gone already.
The heat causes the ice to melt and eventually turn it into gas and disperse it onto the air. Two types of energy involved are the Kinetic Energy (KE), the motion energy which is dependent on the mass and velocity of an object and the Potential Energy (PE), the resting energy or energy due to position and composition. Heat affects KE and said to be directly proportional to each other. As you increase the heat, the temperature increases resulting to an increase on KE. Heat, Temperature, KE and PE are the main factors why do changes on state of matter occur.
Changes are due to evaporation (liquid to gas), freezing (liquid to solid), condensation (gas to liquid), melting (solid to liquid), sublimation (solid to gas) and deposition (gas to solid). All of these processes are result of the changes on the amount of heat added or removed from a certain substance, thereby increasing or decreasing the temperature thru time. Cooling Curve Cooling curve is a graphical representation of the changes of states of substances as heat is uniformly removed from it. At t0 – t1 heat is removed from the gaseous state.
The average KE of the gas particles decreases as the temperature drops until it is reached at t1 where gas starts to liquefy. The temperature at which gas and liquid coexist is called liquefaction or condensation point of the substance, which is just equivalent to boiling point of the heating curve. At this time, the average PE remains constant because there is no change yet on the composition of the gas. At t¬1 – t2 (liquefaction point) there is no change on the average KE of the particles and temperature stays at constant level.
Heat is still being removed causing the decrease on Average PE. Since there is decreasing amount of heat, there is a failure to overcome forces of attraction between particles of the liquid forming gas. The gas particles are compressed and converted into liquid wherein stored PE is released. At this time, the amount of gas decreases while the amount of liquid increases, until reaching t2 where all the gases have been converted to liquid. At t2 – t3, the average KE of the liquid particles decreases and the temperature reaches low level until t3 where the liquid starts to solidify.
Freezing or crystallization of substances occurs at the temperature where liquid and solid coexist. At this point, liquid is no longer a liquid but already turned onto solid state. The molecules of the liquid have been compressed as result of continuous removal of heat from the substance. This time, the average PE continues to decrease because of the amount of heat being removed. Freezing point is just equivalent to melting point in the heating curve. At t3 – t4, there is no change on the average KE and the temperature of the substance stays constant.
Heat is still being removed causing a decrease on average PE of the substance. This time, the amount of liquid decreases and the amount of solid increases until reaching t4 when sufficient heat has been removed thus converting all the liquid into solid. The particles of the substance are oriented properly to form the crystalline lattice at the freezing point. Sometimes, it happens that the heat is continuously removed from the substance without crystallization. At this point, the temperature drops below its freezing point and errors in orienting the particles occur. This phenomenon is learned as Supercooling.
We can reduce supercooling by introduction of a seed crystal for the crystallization to occur and thereby initiating the proper structure. Heating Curve Heating curve is just the opposite of cooling curve. The curve illustrates changes of states of a substance with uniform addition of heat to it. At t0 – t1 heat is added to the solid causing the increase on average KE of its particles. The particles are agitated making them disoriented and result into a slightly less ordered solid state. Temperature rises and at t1, solid starts to melt. T1 is termed as melting point of the substance on which solid and liquid coexist.
At t1 – t2, there is no change on the average KE and the temperature stays constant. Since KE doesn’t change, average PE must increase as heat is continuously added. Now, forces of attraction between particles have been overcome because of high amount of heat. The amount of heat is being stored as potential energy. At this time, amount of solid decreases while the amount of liquid increases. Eventually at t2, sufficient heat has been added to convert the entire solid to liquid. At t2¬ – t3 the average KE and temperature increases. When the increasing temperature reaches t3, the liquid starts to evaporate.
At this temperature (t2), liquid and gas coexist and is termed as boiling point of the substance. At t3 – t4, there is no change in the average KE and temperature remains constant. The force of attraction between liquid particles has been overcome due to addition of more heat. The amount of heat added is still being stored in form of PE. PE increases and the amount of liquid decreases while the amount of gas increases. At t4, sufficient heat has been added to convert all the liquid to gas. As oppose to supercooling, superheating also occurs where liquid is heated to a temperature above its boiling point without evaporation.
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