DOC PREVIEW
PSU CHEM 110 - Thermochemistry

This preview shows page 1-2-16-17-18-34-35 out of 35 pages.

Save
View full document
View full document
Premium Document
Do you want full access? Go Premium and unlock all 35 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 35 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 35 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 35 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 35 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 35 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 35 pages.
Access to all documents
Download any document
Ad free experience
Premium Document
Do you want full access? Go Premium and unlock all 35 pages.
Access to all documents
Download any document
Ad free experience

Unformatted text preview:

Mary J. Bojan Chem 110 Thermochemistry Energy • kinetic • potential First Law of Thermodynamics • ΔE = q + w Enthalpy ΔH Thermochemical Equations Thermochemistry: Study of energy changes in chemical processes 2H2 + O2 → 2H2O + energy 1 ΔH for chemical reactions Calorimetry, Heat Capacity Hess’s Law Heat of formation ΔHf Standard State ΔH°f Foods and FuelsFirst Law of Thermodynamics Law of conservation of energy Energy can be converted from one form to another… …but total energy remains constant. Mary J. Bojan 2 Chem 110Mary J. Bojan Chem 110 Energy Kinetic Energy energy of motion Mechanical moving mass (1/2mv2) Electrical moving charge Light photons Sound molecules moving uniformly Heat molecules moving randomly 3 Potential Energy stored energy Mechanical mass in a place where a force can act Chemical bonds Nuclear binding energyMary J. Bojan Chem 110 Energy H⎯H + H⎯H + O=O → + 3 bonds 4 bonds 4 Electronic Energy The potential energy associated with the electrons in atoms and molecules Chemical energy the Potential Energy associated with bondingMary J. Bojan Chem 110 Changes in Energy w = work= action of force through a distance (often P∆V) work done to the system (+) q = heat (thermal energy) = energy transferred due to a difference in temperature. heat added to the system (+) 5 E = internal energy: total energy (E) associated with a system; the sum of all sources of kinetic & potential energy. the capacity to do work or transfer heat. ΔE =Efinal - Einitial = q + wMary J. Bojan Chem 110 Changes in Energy 6 Energy lost by the SYSTEM … is gained by the SURROUNDINGS. The system: what you are interested in a atom, molecule, or chemical reaction energy System ⎯⎯→ Surroundings ΔE = − energy Surroundings ⎯⎯→ System ΔE = +Mary J. Bojan Chem 110 Energy changes Which one has more energy? Cool the water Heat the water 7Mary J. Bojan Chem 110 State Function a function whose value does not depend on the pathway used to get to the present state State Function: only depends on the current state (composition, T,P): does not depend on past history 8 ΔEMary J. Bojan Chem 110 State Functions State functions are written as uppercase letters (E, H, P, V, T, S…) q and w are not state functions but ∆E (= q + w) is a state function 9 Changes in state functions are path-independentMary J. Bojan Chem 110 Energy (ΔE) and Enthalpy (ΔH) When changes occur at constant pressure ΔE = q + w w = −PΔV = work done on system at constant P arises from expansion or contraction of the system: ΔV = Vfinal – Vinitial ΔE = qp + wexpansion 10 Energy transferred at constant V = ΔEEnthalpy Mary J. Bojan Chem 110 11 quantitative definition: ΔE = qp + wp = qp – PΔV P = constant so qp = ΔE + PΔV ≡ ΔH = Enthalpy qualitative definition: ΔH is heat transferred at constant P For many chemical processes, PΔV is small and Like ΔE, ΔH is a state function.Examples of enthalpy Mary J. Bojan Chem 110 12 physical changes weʼve seen before… " freezing & melting! add heat to ice ⇒" temperature does not change during melting"• " ! vaporizing & condensing! add heat to water ⇒" temperature does not change during vaporization "• "energy transfers accompany:"• " !• " "Mary J. Bojan Chem 110 Thermochemical Equations A balanced chemical equation that also includes the energy change H2(g) + 1/2 O2(g) → H2O(g) ΔH = −241.8kJ ΔH = enthalpy: heat given off or absorbed in the reaction 13Mary J. Bojan Chem 110 ENTHALPY OF REACTION If ΔH<0 (−) exothermic (heat released) If ΔH>0 (+) Endothermic (heat absorbed) 14 ΔH = H(products) – H(reactants)ENTHALPY 1. Enthalpy is an extensive property. 2. ΔH for a reaction is equal in magnitude and opposite in sign to ΔH for the reverse reaction. 3. ΔH for a reaction depends on the states of reactants and products (gas, liquid, solid).Mary J. Bojan Chem 110 How much heat is given off per mole of O2? 16 Is this reaction 1 exothermic 2 endothermic How much heat is given off per mole of H2?Mary J. Bojan Chem 110 How much heat will be needed to convert 9g of water into H2 + O2? 17 How much heat will be given off if liquid water is formed instead of gaseous water. ΔHvap of water = 44kJ/mol If I convert water to H2 + O2, the reaction will be ___________ 1 exothermic 2 endothermic How much heat will be given off if 10g of H2 is consumed?Mary J. Bojan Chem 110 CALORIMETRY Experimental measure of heat flow q = C m ΔT q = heat flow C = specific heat (heat capacity per gram) m = mass ΔT= Tfinal - Tinitial 18 For H2O: C = 4.184 J/g °C Molar heat capacity = 75.2 J/mole °C Note: H2O is usually part of the surroundings qsurr = Csurr m ΔTMeasuring heat of reaction Mary J. Bojan Chem 110 19 Mix 50ml of 1M NaOH + 50ml of 1M HCl What is ΔH°rxn ? = Ti = Tf =Mary J. Bojan Chem 110 Measuring heat of reaction 1. Write the balanced reaction. 2. ΔT = Tf – Ti = 3. Is qp (ΔH°rxn) positive or negative? 4. qp = C m ΔT V=100ml, assume d = 1g/ml Then: m = (100ml)(1g/ml) = 100g qp =(4.184J/goC)(100g) ΔT 20Mary J. Bojan Chem 110 Hess’ Law ΔH for a sum of steps is the same as ΔH for the overall process. 21 True because ΔH is a state function. A → B ΔH1 B → C ΔH2 A+B → B+C ΔH1 + ΔH2 = ΔHrxnMary J. Bojan Chem 110 Hess’ Law Example 22 Given the following information A 2 H2(g) + F2(g) → 2 HF(g) ΔHA = -537kJ B 2 H2(g) + O2(g) → 2 H2O(g) ΔHB = -572kJ Determine ΔH for reaction C C 2 F2(g) + 2 H2O(g) → 4 HF(g) + O2(g) ΔHC = ??? SOLUTION: find combination of reactions such that n A + m B = C Then: n ΔHA + m ΔHB = ΔHCMary J. Bojan Chem 110 Hess’ Law Example 23 Given the following information A 2 H2(g) + F2(g) → 2 HF(g) ΔHA = −537kJ B 2 H2(g) + O2(g) → 2 H2O(g) ΔHB = −572kJ Determine ΔH for reaction C C 2 F2(g) + 2 H2O(g) → 4 HF(g) + O2(g) ΔHC = ??? SOLUTION: 2 A − 1 B = C 2xA 4 H2(g) + 2 F2(g) → 4 HF(g) ΔH = 2x(−537kJ) −1x B 2 H2O(g) → 2 H2(g) + O2(g) ΔH = − (−572kJ) 2 F2(g) + 2 H2O(g) → 4 HF(g) + O2(g) Then: 2 (−537kJ) − 1 (−572kJ) = −502kJMary J. Bojan Chem 110 You try! Given the following information: ΔH 2SO2(g) + O2(g) →


View Full Document

PSU CHEM 110 - Thermochemistry

Documents in this Course
Gases

Gases

12 pages

GASES

GASES

20 pages

Solutions

Solutions

25 pages

REACTIONS

REACTIONS

26 pages

Load more
Download Thermochemistry
Our administrator received your request to download this document. We will send you the file to your email shortly.
Loading Unlocking...
Login

Join to view Thermochemistry and access 3M+ class-specific study document.

or
We will never post anything without your permission.
Don't have an account?
Sign Up

Join to view Thermochemistry 2 2 and access 3M+ class-specific study document.

or

By creating an account you agree to our Privacy Policy and Terms Of Use

Already a member?