Chem notes on reactions
Chem notes on reactions Chem 107
University of Louisiana at Lafayette
Popular in General Chemistry I
Popular in Chemistry
This 2 page Class Notes was uploaded by Alexandra Notetaker on Monday October 17, 2016. The Class Notes belongs to Chem 107 at University of Louisiana at Lafayette taught by Dr. Daniel Rivera in Fall 2016. Since its upload, it has received 5 views. For similar materials see General Chemistry I in Chemistry at University of Louisiana at Lafayette.
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Date Created: 10/17/16
Energy and chemical reactions Energy: capacity to do work o Radiant energy- from the sun o Thermal energy- associated to motion o Chemical energy- associated to molecular bonds o Nuclear energy- associated to o Potential energy- associated to the position of the object Energy changes o Heat-> transfer of energy o Temperature->measure of thermal energy o Thermochemistry-> study of heat change in chemical reactions o A system is the specific part of the universe that is the interest in the study The surrounding is everything else o In a open system: mass and energy exchange o In a closed system: energy exchanges o In an isolated system: nothing is exchanged o Exothermic reaction gives off heat or thermal energy o An endothermic reaction gives of heat of thermal energy o Thermodynamics: scientific study of interconversion of heat and other kinds of energy State functions: properties that are determined by the state of the system regardless of how the condition was achieved (energy, pressure, volume, temp) Delta x = xfinalinitial Laws o First law of thermodynamics: energy is only converted from one form to another but is never created or destroyed Delta (U system) + delta (U surrounding) = zero o Another form of this equation is o Delta (u) = q + w Q is heat exchange and w is work done on or by the system o Work done by the system on the surroundings is measured by force X distance This is not a state function At a constant pressure q= delta H and W= -P delta V Enthalpy o Measure of heat flow into and out of a system at constant pressure This is assuming ideal gas conditions o Enthalpy is products – reactants Delta H = heat given off or absorbed during a reaction at constant pressure Enthalpy is negative in a exothermic reaction and positive in a endothermic reaction o Stoichiometric coefficients always refer to to the number of moles in a system If you reverse a reaction the delta H changes signs If both sides are multiplied by a factor of n, then delta H must change also The physical states of all reactants and products must be specified in the reaction Specific heat o Amount of heat needed to raise the temperature of one gram of substance by one degree celcius o Heat capacity: substance is amount of heat required to raise the temperature of given quantity of substance by now degree celcius Constant volume calorimetry o Measure different temperatures after combustion has occurred/ uses water (poor conductor) Constant pressure calorimetry o Reaction occurs with a Pressure o Measures changes in enthalpy Acid-bases reactions are generally exothermic o Before any calculation can be done, must first write the neutralization reaction o Then write the specific heats of the products – the specific heat of the reactants o You may have to convert from grams to moles using the reaction equation Standard enthalpy of formation o Used as a reference point for enthalpy expression o Delta H 0f o SEF is the heat change that results when 1 mole of a compound is formed from its elements at a pressure of 1 atm o SEF of any element in its most stable form zero o Sum of SEF of the products – the SEF of the reactants o The charge in the enthalpy is the same whether or not it happens in one step or two steps or many steps : state function o Eliminate spectators from reactants and products Manipulating the given equations to look at the give main equation add up the calculated #’s
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