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  Heat and properties of matter, Physics tutorial

Introduction:

Heat:

Heat energy which is transferred from one body to another because of difference in temperature. If two bodies at different temperatures are brought together, energy is transferred-that is heat flows-from hotter body to colder. The effects of this transfer of energy generally, but not always, is the increase in temperature of colder body and the decrease in temperature of hotter body. The substance may absorb heat without the increase in temperature by changing from one physical state (or stage) to another, as from the solid to liquid (melting), from solid to vapor (sublimation), from the liquid to a vapor (boiling), or from one solid form to another (generally known as a crystalline transition). Significant distinction between heat and temperature (heat being the form of energy and temperature a measure of amount of that energy present in the body) was clarified during 18th and 19th centuries.

Heat as a form of energy:

As all of the several forms of energy, comprising heat, can be converted in work, amounts of energy are stated in units of work, like joules, foot-pounds, kilowatt-hours, or calories. Exact relationships exist between amounts of heat added to or removed from the body and magnitude of the effects on state of body. Two units of heat most usually utilized are calorie and British thermal unit (BTU). Calorie (or gram-calorie) is amount of energy needed to raise temperature of one gram of water from 14.5° to 15.5° C; the BTU is amount of energy needed to increase temperature of one pound of water from 63° to 64° F. One BTU is around 252 calories. Both definitions state that temperature changes are to be estimated at the constant pressure of one atmosphere, as amounts of energy involved depend in part on pressure. Calorie utilized in estimating energy content of foods is large calorie, or kilogram-calorie, equal to 1,000 gram-calories.

Generally, amount of energy needed to increase the unit mass of the substance through the specified temperature interval is known as heat capacity, or specific heat, of that substance. Quantity of energy essential to increase the temperature of the body one degree differs relying on restraints imposed. If heat is added to the gas confined at constant volume, amount of heat required to cause one-degree temperature rise is less than if heat is added to same gas free to expand (as in the cylinder fitted with movable piston) and so do work.

Matter:

Matter is expressed as anything which occupies space and has mass. Mass is the measure of the object's inertia. It is proportional to weight: more mass an object has, the more weight it has. Though, mass is not the same as weight.

States and properties of Matter:

One significant physical property is state of matter. They are common in everyday life: solid, liquid, and gas. Fourth, plasma, is seen in special conditions like ones found in sun and fluorescent lamps. Substances can exist in any of states. Water is the compound which can be liquid, solid (ice), or gas (steam).

Solids:

Solids have the definite shape and definite volume. Most everyday objects are solids: rocks, chairs, ice, and anything with the particular shape and size. Molecules in the solid are close together and connected by intermolecular bonds. Solids can be amorphous, means that they have no specific structure, or they can be arranged in crystalline structures or networks. For example, soot, graphite, and diamond are all composed of elemental carbon, and they are all solids. Soot is amorphous, so atoms are randomly stuck together. Graphite forms parallel layers which can slip past each other. Diamond, though, forms the crystal structure which makes it very strong.

Liquids:

Liquids have the definite volume, but they don't have the specific shape. Instead, they take shape of the container to extent they are indeed contained by something like beaker or the cupped hand or even a puddle. If not contained by the formal or informal vessel, the shape is found by other internal (like intermolecular) and external (like gravity, wind, inertial) forces. Molecules are close, but not as close as a solid. Intermolecular bonds are weak, so molecules are free to slip past each other, flowing smoothly. The property of liquids is viscosity, measure of thickness when flowing.

Gases

Gases have no specific volume and no specific shape. They inflate to fill size and shape of their container. Oxygen which we breathe and steam from the pot are both examples of gases. Molecules are very far apart in the gas, and there are minimal intermolecular forces. Every atom is free to move in any direction. Gases go through effusion and diffusion. Effusion takes place when the gas seeps through small hole, and diffusion takes place when the gas spreads out across room. If one leaves the bottle of ammonia on the desk, and there is a crack in it, ultimately whole room will reek of ammonia gas. This is because of diffusion and effusion. These properties of gas take place as molecules are not bonded to each other.

Physical Properties:

Physical properties are properties which can be estimated or seen without changing chemical nature of the substance. Few examples of physical properties are:

  • color (intensive)
  • density (intensive)
  • volume (extensive)
  • mass (extensive)
  • boiling point (intensive): temperature at which the substance boils
  • melting point (intensive): temperature at which the substance melts.

Chemical Properties:

Chemical property is that measuring that property should lead to the change in substance's chemical structure. Numerous examples of chemical properties are given below:

  • Heat of combustion is energy released when the compound goes through complete combustion (burning) with oxygen. Symbol for heat of combustion is ΔHc.
  • Chemical stability refers to whether the compound will react with water or air (chemically stable substances won't react). Hydrolysis and oxidation are two such reactions and are both chemical changes.
  • Flammability refers to whether the compound will burn when exposed to flame. Burning is the chemical reaction-usually the high-temperature reaction in presence of oxygen.
  • Preferred oxidation phase is the lowest-energy oxidation state which the metal will go through reactions to get (if another element is present to accept or donate electrons).

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