Chem notes April 19
Chem notes April 19 Chemistry 1030
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This 3 page Class Notes was uploaded by Emma Shoupe on Wednesday April 20, 2016. The Class Notes belongs to Chemistry 1030 at Auburn University taught by Dr. Livia Streit in Spring 2016. Since its upload, it has received 13 views. For similar materials see General Chemistry 1 in Chemistry at Auburn University.
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Date Created: 04/20/16
General Chemistry I – Week of April 17, 2016 Chapter 10 – Energy Changes in Chemical Reactions System- a part of the universe that is of specific interest Surroundings- rest of the universe outside of the system Thermochemistry- study of heat in chemical reactions Heat- transfer of thermal energy o Either absorbed or released o SI unit is a Joule, J o Calories are often used – amount of heat required to raise 1g of water by 1 degree Celsius o 1 cal = 4.184 J exothermic process- occurs when heat is transferred from the system to the surroundings endothermic process – occurs when heat is transferred from the surroundings to the system thermodynamics – study of the interconversion of heat and other kinds of energy o 3 types of systems open system- can exchange mass and energy with the surroundings closed system- allows the transfer of energy but not mass isolated system- does not exchange either mass or energy with its surroundings state functions- properties that are determined by the state of the system, regardless of how that condition was achieved o pressure o volume o temperature o energy First Law of thermodynamics- energy can be converted from one form to another, but not created nor destroyed Pressure- volume or PV work- done when there is a volume change under constant pressure The difference between ΔH and ΔE is the amount of work (PΔV) done by the system. The volume change for most reactions is close to zero, which makes PΔV very small, and therefore the difference between ΔH and ΔE very small. It is generally satisfactory to use ΔH as the measure of energy changes during most chemical processes. Enthalpy of reaction- the difference between the enthalpies of the products and the enthalpies of reactants o ΔH rxn = Σ ΔH froducts - Σ ΔH rfactants o if H < 0 = exothermic o if H > 0 = endothermic Enthalpy (ΔH) – the heat, qp, gained or lost by the system when the process occurs at constant pressure (which most reactions do). Endothermic - When the system absorbs heat from the surroundings and the surroundings get cold. (+ ΔH) Exothermic - When the system releases heat to the surroundings and the surroundings get hot. (- ΔH) enthalpy is an extensive property extensive properties – dependent on the amount of matter involved Thermochemical equations: o Specify physical states of reactants and products o Multiply ∆H value by the same factor used to multiply the equation o Reversing an equation changes the sign of ∆H, but not the magnitude Calorimetry – measurement of heat changes Calorimeter – apparatus that measures heat flow by measuring changes of temperature of a known amount of water Specific heat- amount of heat required to raise 1g of a substance 1 degree Celsius Heat capacity- amount of heat required to raise an entire substance 1 degree Celsius q = mcΔT where m = mass (g), c = specific heat (J/g · °C), T = change in temp. (either °C or K) ΔT = T f T i exothermic reaction- system loses heat, surroundings gain heat Hess’s Law – states the change in enthalpy for a stepwise process is the sum of the enthalpy changes for each of the steps Standard enthalpies of formation- the heat change that results when 1 mole of a compound is formed from its constituent elements in their standard states o ΔH = heat of formation f o heat of formation is the heat change when a compound is formed from the elements Enthalpy is an extensive property meaning it is dependent upon the amount of substance present. This means the ΔH must fe multiplied by the coefficient in the balanced equation. Bond enthalpy- enthalpy change associated with breaking a bond in 1 mole of a gaseous molecule o ΔH rxn = Σ Bond Energies of Bonds Broken - Σ Bond Energies of Bonds Formed
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