# Chapter 5 - The study of energy and it's changes The study...

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The study of energy and it's changes The study of relationship between chemical reaction and energy (E) changes involving heat Is capacity to do work or transfer heat Energy required to move an object with mass W= force X distance Energy used to cause temperature of object to increase (from hot to cold) Push or pull exerted on an object. Gravity!

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Part of universe we are interested in studying Rest of universe 2H2 + O2 -> 2H2O = system Everything else = surroundings

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Absorbs heat (feels cool) Transfers heat to surroundings (feels hot) Specific chemical reaction that is endothermic or exothermic flow of heat in & out of system

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H product - H reactants Enthalpy of reaction Amount of energy required to increase temp of substance by 1OC or 1K Same symbol Cmolar heat capacity of 1 mole of substance Heat capacity of one gram of substance Quantity of heat transferred Grams of substance X ∆T S= q/(m * ∆T)

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Unformatted text preview: q= s*m*∆T If reaction takes place through many steps, ∆Hrxn-overall, equal to sum of the ∆H for each step. Enthalpy is a state function Gaseous water --> water, negative value for heat loss Step 1 Exothermic Exothermic Step 2 CH4 (g) + 2O2 + 2H2O (g) -->CO2 (g) + 2H2O (g) + 2H2O(l) ∆Hrxn = ∆H2 + ∆H3 = -607 + -283 = -890 Enthalpy of formation ∆Hf 1 atm of pressure, 25OC = 298K Change of ∆HO when everything is in the standard state Enthalphy change for the formation of 1 mole of compound ∆H f O for the most stable form = 0, ex. H 2 (g), O 2 (g), C graphite 1. C 3 H 8-> 3C (s) + 4H 2(g) ∆H 1 = -∆H F O [C 3 H 8 ] 2. 3C (s) + 3O 2(g)-> 3CO 2(g) ∆H 2 = 3∆H F O [CO 2 ] 3. 4H 2(g) + 2O 2(g)-> 4H 2 O (l) ∆H 3 = 4∆H F O [H 2 O (l) ] ∆Horxn = ∆H1 + ∆H2 + ∆H3 =-(-103.85KJ/mol) + 3(-393KJ/mol) + 4(-285KJ/mol) =-2220 KJ/mol...
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