Enthalpy 1105.

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Presentation transcript:

Enthalpy 1105

What are we going to do today? NaOH + H2O  -OH + Na+ HCl + H2O  H3O + + Cl- HCl + NaOH → H2O + Na+ Cl- + Heat Today we will look at the products Measure quantity of heat transferred in a system. And to measure heat we use: Q

Enthalpy You can only measure the change in enthalpy State Function Energy Change Per Mole Think of it like the energy in the bonds State Function Depends only on the current state of the system (comp., vol., temp., etc) Independent of the path only initial and final Energy content of a system The increase in enthalpy of a system is equal to the added heat So…… ∆H = Q =Heat of Reaction

Enthalpy ∆H = HP – HR From the Graph Would ∆H be “-” or “+”? ∆H = “-” Exothermic (HR > HP) Heat is produced ∆H H HR HP R → P (Progress)

Enthalpy Endothermic ∆H = “+” Hp > Hr Heat is absorbed

Important Thermodynamics Gibbs free energy (SUPER IMPORTANT TO KNOW) ∆G= ∆H - T ∆S Enthalpy = H Heat Transferred Entropy = S measure of disorder Temperature = T Gibbs free Energy = E exchange State Function Property of a system dependent only on its current state Depends only on the initial and final state

Experiment Our Goal: Determine heat of reactions Must Determine Heat Product To Give The ∆H Q = Amount Of Heat Transferred In A Reaction MicroLab R P Universe Surrounding System Stirrer

Objective of the exp. Solvation NaOH solid in water = Do not throw away this solution you will needed for exp.3 Neutralization HCl (aq) and NaOH (aq) equal concentration Reaction NaOH (solid ) + in HCl (aq) So… In theory 1 + 2 ≈ 3

Experiment QSurr. = - QSys. Will measure the amount of heat transfer Remember Qsurroundings? Q= S.H. * m * ∆T Since the density of water is one QSurr. = S.H. * (d * V) * ∆T QSurr. = - QSys. In order for surrounding to gain energy, system had to lose energy

Calculations 1 calorie = 4.184 joules Molarity NaOH = mol / L So…Molarity * volume in L = mol ∆H = QSys. in KJ / mols NaOH Exothermic is – endothermic is+ Don not throw your first solution you are going to need it for exp. 3 mL 1.00 g Total mL change T OC - 4.184 J g O