Standard Enthalpy of Formation EQ: Why does the  Hfº for a free element equal zero?

Slides:

Advertisements

Similar presentations

Topic c Bond energies and Enthalpies

Advertisements

Catalyst Given the following equations and H o values, determine the heat of reaction (kJ) at 298 K for the reaction: B 2 H 6 (g) + 6 Cl 2 (g)  2 BCl.

Standard Enthalpy (Ch_6.6) The heat change that results when 1 mole of a compound is formed from its elements at a pressure of 1 Atm.

Thermodynamics Chapter 19 Liquid benzene Production of quicklime Solid benzene ⇅ CaCO 3 (s) ⇌ CaO + CO 2.

CHEMISTRY 161 Chapter 6

© 2006 Brooks/Cole - Thomson Some Thermodynamic Terms Notice that the energy change in moving from the top to the bottom is independent of pathway but.

Enthalpy EQ: How do you predict the sign of delta H?

Using Standard Molar Enthalpies of Formation SCH4U0.

 Enthalpy changes also occur when a compound is formed from elements.  Standard enthalpy of formation, ΔHº f, is the heat released or absorbed when one.

Bomb Calorimetry constant volume often used for combustion reactions heat released by reaction is absorbed by calorimeter contents need heat capacity of.

Standard Molar Enthalpies of Formation ΔHfoΔHfo. Focus Questions 1) What are formation reactions? 2) What is standard molar enthalpy of formation? 3)

Energetics IB Topics 5 & 15 PART 2: Calculating  H via Bond Enthalpies & Hess’s Law Above: thermit rxn.

Thermochemistry Chapter 5. First Law of Thermodynamics states that energy is conserved.Energy that is lost by a system must be gained by the surroundings.

 Section 1 – Thermochemistry  Section 2 – Driving Force of Reactions.

Enthalpy (H) The heat transferred sys ↔ surr during a chemical constant P Can’t measure H, only ΔH At constant P, ΔH = q = mCΔT, etc. Literally,

Stoichiometry II. Solve stoichiometric problems involving moles, mass, and volume, given a balanced chemical reaction. Include: heat of reaction Additional.

Thermochemistry THERMOCHEMISTRY THERMOCHEMISTRY, is the study of the heat released or absorbed by chemical and physical changes. 1N = 1Kg.m/s 2, 1J =

The study of the heat flow of a chemical reaction or physical change

It has been suggested that hydrogen gas obtained by the decomposition of water might be a substitute for natural gas (principally methane). To compare.

Chapter 8 Thermochemistry. Thermodynamics  Study of the changes in energy and transfers of energy that accompany chemical and physical processes.  address.

Thermochemical equations Thermochemical equations  Thermochemical equation = a balanced chemical equation that includes the physical states.

Topic: Thermodynamics Do Now: packet p.1. Every physical or chemical change is accompanied by energy change  Energy released = _________________  Energy.

1.2.2 Heat of Formation.  Standard Heat of Formation Δ H o f  the amount of energy gained or lost when 1 mole of the substance is formed from its elements.

Section 7.4—Energy of a Chemical Reaction What’s happening in those hot/cold packs that contain chemical reactions?

THERMOCHEMISTRY Inneke Hantoro. INTRODUCTION Thermochemistry is the study of heat changes in chemical reactions. Almost all chemical reactions absorb.

Unit 8 - Stoichiometry. 2CuCl + H 2 S → Cu 2 S +2HCl The coefficients in the equation can either mean particles or moles.

Thermochemistry Mrs. Stoops Chemistry.

Mullis1 First Law of Thermodynamics (Law of Conservation of Energy) The combined amount of matter and energy in the universe is constant. The combined.

Standard Heats of Reaction The value of  H for a reaction depends on the temperature and pressure so scientists have agreed upon a set of reference conditions.

CHM 108 SUROVIEC SPRING 2014 Chapter 6 Energy Transfer.

More Heat Calculations What have we done?. We can figure out heat values and then put them into kJ / mole.

Thermochemistry ENERGY CHANGES.. Energy is the capacity to do work Thermal energy is the energy associated with the random motion of atoms and molecules.

Thermochemistry Chapter 6 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

A Comparison of  H and  E 2Na (s) + 2H 2 O (l) 2NaOH (aq) + H 2 (g)  H = kJ/mol  E =  H - P  V At 25 0 C, 1 mole H 2 = 24.5 L at 1 atm P 

THERMOCHEMISTRY CP Unit 9 Chapter 17.

SCH4U Thermodynamics. * Energy difference between the reactants and products. ΔH = H products - H reactants As long as pressure remains constant, the.

Friday, Oct. 25 th : “A” Day Monday, Oct. 28 th : “B” Day Agenda  Homework questions/Quick review  Section 10.2 Quiz: “Using Enthalpy”  Section 10.3:

Chemistry 1011 Slot 51 Chemistry 1011 TOPIC Thermochemistry TEXT REFERENCE Masterton and Hurley Chapter 8.

CHM 102 Sinex Enthalpy. CHM 102 Sinex Enthalpy (H) ~ heat content constant pressure  H = thermal (heat) energy change = q H 2 O (l) + energy 

 Section 1 – Thermochemistry  Section 2 – Driving Force of Reactions.

STANDARD HEAT OF FORMATION. DEFINITION The change in enthalpy that accompanies the formation of one mole of the compound at its normal state from its.

Thermochemistry Standard Enthalpies of Formation.

Standard Enthalpy of Formation Chapter 5.5 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Energy & Rates.

enthalpy of formation (DHf): the enthalpy change

Communicating Enthalpy Change. Method 1: Molar Enthalpies of Reaction, Δ r H m To communicate a molar enthalpy, both the substance and the reaction must.

Heat in Changes of State. What happens when you place an ice cube on a table in a warm room? Molar Heat of Fusion (ΔH fus ): heat absorbed by one mole.

Formation Reactions Examples: C (s) + O 2(g)  CO 2(g) Na (s) + ½ Br 2(l)  NaBr (s) 6C (s) + 6H 2(g) + 3O 2(g)  C 6 H 12 O 6(s)

Thermochemistry Heats of Formation and Calculating Heats of Reaction.

Thermochemistry Chapter 6. Thermochemistry is the study of heat change in chemical reactions.

It is impossible to measure enthalpy directly

Thermochemistry Part 4: Phase Changes & Enthalpies of Formation.

Enthalpies of Formation and Reaction Definitions: Standard state –A gas at 1 atm –An aqueous solution with a concentration of 1 M at a pressure of 1 atm.

Thermochemistry. Thermodynamics  Study of the changes in energy and transfers of energy that accompany chemical and physical processes.  address 3 fundamental.

PRACTICE PROBLEMS Sample Problem Calculate the enthalpy change for the reaction in which hydrogen gas, H 2 (g), is combined with fluorine gas, F 2(g),

Thermochemistry Exothermic process is any process that gives off heat – transfers thermal energy from the system to the surroundings. Endothermic process.

Heat of Formation If you understood Hess’ Law, you will have NO problem here.

Exothermic  When heat is released (given off) by the system into the surroundings, the process is exothermic  H = H final − H initial  H = H products.

Thermodynamics. Every physical or chemical change is accompanied by energy change Thermodynamics = branch of chemistry that studies energy changes –Specifically:

© 2009, Prentice-Hall, Inc. Enthalpies of Formation An enthalpy of formation,  H f, is defined as the enthalpy change for the reaction in which a compound.

Chapter 5 Thermochemistry. Thermodynamics  Study of the changes in energy and transfers of energy that accompany chemical and physical processes.  address.

Stoichiometry and ∆H (Honors)

Heats of Formation.

Calculating ΔH using molar heats of formation

Enthalpy of formation - ΔHºf

Thermochemistry Part 2 – enthalpy.

AP Chem Get Heat HW stamped off Today: Enthalpy Cont., Hess’ Law

Thermodynamics Heat of Formation.

Rate Law (Honors) Mathematical expressions relating the rate of reaction to the concentration of reactants. Rate of a reaction can only be determined from.

THERMODYNAMICS #1 Example of using standard heats of formation to get ∆H of reaction Calculate the heat of reaction for the following combustion. 4 NH3.

Section 7.4—Energy of a Chemical Reaction

Presentation transcript:

Standard Enthalpy of Formation EQ: Why does the  Hfº for a free element equal zero?

A. Standard Enthalpy of formation (  H f º)  H f º : the energy change that occurs when 1 mole of a compound is formed (most are negative) A.Standard conditions = 25ºC & 1 atm (gases) & 1 Molar (aqueous solutions) B.values found in table or appendix C (pg 921) C.All free elements in their most stable form  H f º= zero Since you can not make elements This includes diatomics (Cl 2, H 2, O 2, etc.)

A. Standard Enthalpy of formation (  H f º)  Ex: reaction for the heat of formation for H 2 O (g)  Elements in water = H and O  Stable form = H 2 and O 2  H 2 (g) + ½ O 2 (g)  H 2 O (g)  H f º= kJ/mol

B. Calculating  Hrxn The  Hºrxn can also be found using the  H f º values  use coefficients in the balanced reaction  pay attention to states (s, l, g, aq)  Hºrxn =  n  H f º(products) -  n  H f º (reactants) n= moles  (sigma) = sum of

Example 1 Use the standard enthalpies of formation on pg 510 to calculate  Hº rxn for: 4NH 3 (g) + 7O 2 (g)  4NO 2 (g) + 6H 2 O (l)  Hº rxn = [ (4 mol x 33 kJ/mol) + (6 mol x -286 kJ/mol)] - [(4 mol x -46 kJ/mol)+ (7 mol x 0 kJ/mol)]  Hº rxn = [132 kJ kJ] - [-184 kJ + 0kJ] = kJ. Round to the least number of decimal places out of all of the table values (free element) From table

Example 2 Use the table on pg 921 and the reaction below to determine the standard enthalpy of formation for CCl 4 gas. CH 4 (g) + 4Cl 2 (g)  CCl 4 (g) + 4HCl(g) ∆H  = –397 kJ ∆H rxn =[(1 mol x ∆H f  CCl 4 (g)] + (4 mol x –92.307kJ/mol)] - [(1 mol x kJ/mol) + (4 mol x 0 kJ/mol)] [1 mol ∆H f  kJ ] - [ kJ] -397 kJ = ? (gas)  From table

Example 2 (continued) [ 1 mol ∆Hf  kJ ] - [ kJ]-397 kJ = 1 mol ∆Hf  kJ -397 kJ = kJ = 1 mol ∆Hf  1 mol ∆Hf  = -103 kJ/mol

Ex 3: Benzene (C 6 H 6 ) burns in air to produce carbon dioxide and liquid water. How much heat is released per mole of benzene combusted? The standard enthalpy of formation of benzene is kJ/mol. 2C 6 H 6 (l) + 15O 2 (g) 12CO 2 (g) + 6H 2 O (l) H0H0 rxn n  H 0 (products) f =  n  H 0 (reactants) f  - H0H0 rxn 6  H 0 (H 2 O) f 12  H 0 (CO 2 ) f = [+] - 2  H 0 (C 6 H 6 ) f [] H0H0 rxn = [ 12x– x– 286 ] – [ 2x49.04 ] = kJ kJ 2 mol = kJ/mol C 6 H 6