10-4 Enthalpy (Section 10.6) And you.

Slides:



Advertisements
Similar presentations
Spring Semester Final Exam Review
Advertisements

CDO Chemistry Thermodynamics 1 st Law of Thermodynamics 1 st Law – energy cannot be created or destroyed it can just change forms Energy can be.
 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.
Energy Changes in Reactions. Aims of lesson: To discuss energy changes in chemical reactions. To draw potential energy diagrams for exothermic and endothermic.
Thermodynamics Unit 10. Endothermic vs. Exothermic Endo – chemical absorbs or takes in energy or heat Exo – chemical produces or gives off energy or heat.
Notes on Heat. Nomenclature “Heat” can mean several different things Sometimes it used to mean “energy” (sloppy) Sometimes it is “hotness” (i.e temperature)
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.
Energy Transformations Thermochemistry is the study of energy changes that occur during chemical reactions and changes in state. The energy stored in the.
Thermochemistry. Kinetic Energy and Potential Energy Kinetic energy is the energy of motion: Potential energy is the energy an object possesses by virtue.
Thermochemistry Chapter 6. The Nature of Energy Energy is the capacity to do work or produce heat. Energy is the capacity to do work or produce heat.
Chapter 6 Thermochemistry. 6.1: I. Nature of Energy A. Energy (E): capacity for work or producing heat B. Law of Conservation of Energy: can’t be created.
Unit 1: Energy Changes in Chemical Reactions Not All Reactions Go Off with a Bang!
Key Terms Average kinetic energy - Energy associated with the movement of matter and mass Bond energy - The amount of energy it takes to break one mole.
Heat in Chemical Reactions Ch. 16. Energy in Chemical Reactions Every reaction has an energy change associated with it Energy is stored in bonds between.
Thermochemistry. Thermodynamics - study of energy and its transformations Thermochemistry - study of chemical reactions involving changes in heat.
Chapter 5 Thermochemistry
Thermochemistry.
Describe how a chemical reaction happens
HEAT IN CHEMICAL REACTIONS
Chapter Ten Energy Changes in Chemical Reactions
Thermochemistry Study of energy changes that occur during chemical reactions and changes in state.
Enthalpy Calculating Heats of Reaction
Chapter 16: Energy and Chemical Change
Thermodynamics.
Calorimetry and Enthalpy
Enthalpy and Thermochemical Equations
Things are “heating up” now!
10-4 Enthalpy (Section 10.6) And you.
Thermochemistry Chapter 5.
Change in Enthalpy Unit 11.
Chemical Reaction Energy
Warm up How many calories are in 535 kJ?
AP Chem Tests have been graded; you may start coming in to do test corrections. There was a typo in the FRQ section so I’ll add in the points back for.
University of North Carolina, Wilmington
Energy of Reactions Chemistry 11.
Heat of Reactions.
Energy Chapters 3,4,5,6.
Can you guess the topic for today?
Thermochemistry Chapter 6.
Thermodynamics.
Enthalpy of formation - ΔHºf
Thermochemistry Chapter 6.
Unit 1: Reaction Kinetics
Heat in Chemical Reactions and Processes
Unit 12 Thermochemistry.
Welcome to CH104 – General Chemistry
Intro to chemistry Therm o breaking forming
It was a hot summer day. Mattie poured herself a glass of lemonade
Chapter 6 Thermochemistry
Flashcards for Unit 13.
Bell Ringer May 11th The law of conservation of energy: energy cannot be ________ or _______. It can only be ________ or __________.
Energy Changes in Reactions
Chapter 7.1 – Nature of Chemical Reactions
Heat and the Enthalpy of Reaction
Topic 16: Energy and Chemical Change
Energetics 6.1 What is Energetics?
Energy Changes.
Bond energies.
Chapter 16 Preview Objectives Thermochemistry Heat and Temperature
Heat and the Enthalpy of Reaction
THERMOCHEMISTRY Thermodynamics
Chapter 5 Thermochemistry Part B
ENERGETICS /THERMOCHEMISTRY (AS)
Ch. 17: Reaction Energy and Reaction Kinetics
Heat of Reaction & Enthalpy
Heat and the Enthalpy of Reaction
Thermodynamics.
7.3 Energy Changes In Reactions
Chapter 16 Preview Objectives Thermochemistry Heat and Temperature
The study of heat released or required by chemical reactions
Presentation transcript:

10-4 Enthalpy (Section 10.6) And you

Enthalpy, symbolized by H, can be thought of as the potential energy stored in the bonds of molecules. Chemists use the change in enthalpy ∆H to measure the heat content of a system (when the pressure is constant). We define the “system” to be the chemicals and everything else is termed the “surroundings”. Applying the First Law of Thermodynamics (Conservation of Energy), any heat lost by the system will equal the heat gained by the surroundings (and vice versa). Exothermic (“exo” means released or “exits” and therm refers to heat)

Exothermic reactions characteristics Reactants: high E (H), less stable, weak bonds Products: low E (H), more stable, strong bonds System releases PE from bonds to KE of surroundings (which feel hot). ∆H = P – R = negative value (heat released)

Endothermic (“endo” means absorbed or “going in” and therm refers to heat)

Characteristics: Reactants: low E (H), more stable, strong bonds Products: high E (H), less stable, weak bonds System absorbs KE from surroundings as PE in the bonds. Surroundings will feel cold. ∆H = P – R = positive value (heat absorbed)

Bond Energies and ∆H: It requires energy to break the bonds of the reactants. It releases energy when new bonds of the products form. The difference between these two energies is the ∆H. Note, though, if: Energy absorbed to break reactants > Energy released forming products Endo ∆H = +  Energy absorbed to break reactants < Energy released forming products Exo ∆H = -

Example ½ H2 + ½ Cl2  HCl Think of bond energies as KE entering or leaving the system. 216 + 120  427 The change in KE = the change in PE  91 H = -91kJ/mol Exothermic

10-5 Enthalpy of Formation The enthalpy of formation, ∆Hf, is defined as the heat absorbed or released when making 1 mole of a compound from its elements (at 25oC and 1 atm). By convention, the Hf of any element at this temperature and pressure is zero.

Reaction Hf (kJ/mol) Stability of Product ½ N2(g) + 3/2 H2(g) → NH3 -46 stable ½ N2(g) + O2 → NO2 +34 unstable 2 Al + 3/2 O2 → Al2O3 -1676 very stable

10-6 Enthalpy of a Rection H = ∑Hf (products) – ∑Hf (reactants) Hc = enthalpy of combustion ~ defined for the combustion of 1 mole of a fuel  CH4(g) + 2O2(g) → CO2(g) + 2H2O(l)  [-393.5 + 2•(-285.8)] – [-74.8] = -890.3 kJ/mol Burning fuels is always exothermic Hc = Hrxn