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If q is positive, we saythat the reaction is endothermic, that is, heat flows into the reaction from the outside surroundings. W is the work being done on the system in joules Q is the heat flowing into the system in joules Mathematically, we can look at the change in energy of a system as being a function of both heat and work:ĭE is the change in internal energy of a system, in joules Heat is defined as that energy that is transferred as a result of a temperature difference between a system and its surroundings. Chemically, that usually means energy is converted to work, energy in the form of heat moves from one place to another, or energy is stored up in the constituent chemicals. w = dV x PĮxample Problem: Calculate the work that must be done at standard temperature and pressure (STP is 0 degrees C and 1 atm) to make room for the products of the octane combustion:ĮnergyYou might remember the first law of thermodynamics: energy cannot be created or destroyed. If we imaginea reaction taking place in a container of some volume, we measure work bypressure times the change in volume. The value of distance times area is actually the volume. In chemical reactions, work is generally defined as : W = work, in joules (N*m) (or calories, but we are using primarily SIunits) Heat of fusion is the heat required to melt a substance at is normal melting temperature, while the heat of vaporization is the heat required to evaporate the substance at its normal boiling point.Ĭhemical work is primarily related to that of expansion. Two other common heat variables are the heat of fusion and the heat of vaporization. The values for specific heat that are reported in the literature are usually listed at a specific pressure and/or volume, and you need to pay attention to these settings when using values from textbooks in problems or computer models.Įxample Problem: If a 2.34 g substance at 22 degrees celsius with aspecific heat of 3.88 cal/g☌ is heated with 124 cal of energy,what is the new temperature of the substance? The value of C for water is 1.00 calories/gram-degrees Celsius. Specific heat, given by the symbol "C", is generally defined as:Ĭ = specific heat in calories/gram-degrees Celsiusĭelta T = rise in temperature of the material in degreesCelsius. Youwill also encounter the term specific heat, the heat required to raise one (1) gram of a material one (1) degree Celsius. One calorie of heat is equivalent to 4.187 J. Typically, we use the SI units of Joules (J) andkilojoules (kJ). Heat energy is measured in kilocalories, or 1000 calories. Work and heat can both be described using the same unit of measure.Sometimes the calorie is the unit of measure, and refers to the amountof heat required to raise one (1) gram of water one (1) degree Celsius. Work can be transformed into heat, such as might be experienced by rubbing your hands together to warm them up. Heat energy (such as steam engines) can be used to do work (such as pushing a train down the track). They are also related forms, in that one can be transformed into the other. Heat and WorkHeat and work are both forms of energy. Thermodynamics can be roughly encapsulated with these five (5) topics: The term itself clearly suggests what is happening - "thermo", from temperature, meaning energy, and "dynamics", which means the change over time. Thermodynamics is the study of energy changes accompanying physcial and chemical changes. are clearly physical events that also have a chemical nature to them. Certainly changes in energy - however measured, whether it be heat, light, work, etc. Physics concerns itself heavily with the mechanics of events in nature. The scientific discipline that intersects the areas of chemistry andphysics is commonly known as physical chemistry, and it is in that area that a thorough study of thermodynamics takes place.
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