Enthalpy of Chemical Reactions CHEMISTRY 11 Feb. 16, 2010.

Slides:



Advertisements
Similar presentations
Reaction Rates (cont.) Energy in a Reaction (p.11)
Advertisements

UNIT VI Types of Chemical Reactions. VI.5 TYPES OF CHEMICAL REACTIONS When we classify reactions by how atoms are rearranged, there are 5 MAJOR TYPES.
TICKET TIME TEST REVIEW 1. 1 HOW MANY ATOMS ARE IN THIS MOLECULE? 3.
Endothermic Vs. Exothermic Reaction Graphs. Endothermic Reaction: a reaction in which the products have more stored energy than the reactants. The reaction.
Page 34 In a chemical reaction, bonds in the reactants are broken and the atoms rearrange to form new bonds in the products. Flames or heat associated.
Enthalpy and Heat of Reaction. Basic Info All chemical reactions involve energy changes, whether energy is being absorbed or given off. Where does this.
3.3 – Enthalpy and Heat of Reaction. Basic Info: All chemical reactions involve energy changes, whether energy is being absorbed or given off. Where does.
Energy Changes in Reactions. Aims of lesson: To discuss energy changes in chemical reactions. To draw potential energy diagrams for exothermic and endothermic.
ENDOTHERMIC AND EXOTHERMIC REACTIONS. EXOTHERMIC REACTIONS Chemical Reactions that RELEASE heat with the products. You may see an exothermic reaction.
Exothermic and Endothermic Reactions. Exothermic reactions An exothermic reaction is a chemical change that releases energy. Where does the energy that.
{ Exothermic & Endothermic REACTIONS Energy in Reactions.
Rates of Reaction Mrs. Coyle. How fast does aging occur?
Section 1Chemical Reactions 〉 When do chemical reactions take place? 〉 Chemical reactions occur when substances undergo chemical changes to form new substances.
KEY CONCEPT Life depends on chemical reactions.
Section 1Chemical Reactions 〉 When do chemical reactions take place? 〉 Chemical reactions occur when substances undergo chemical changes to form new substances.
Energy Changes & Reactions Unit 7 - Chapter 7.3. Chemical Bonds and Energy  Chemical reactions:  Breaking chemical bonds in the reactants  Forming.
THERMOCHEMISTRY CP Unit 9 Chapter 17.
Chapter 16 Chemical Reactions That Involve Heat. The study of the changes in heat in chemical reactions. Thermochemistry.
Bond Enthalpies 5.4.  Chemical reactions involve the breaking and making of bonds.  To understand the energy changes in a chemical reaction, we need.
ENERGY EXCHANGES IN CHEMICAL REACTIONS
Exothermic and Endothermic Reactions. - What is Exothermic and Endothermic Reactions ? Exothermic reactions : Reactions accompanied with producing heat.
Bond Enthalpy Chem 12. The enthalpy change required to break a particular bond in one mole of gaseous molecules is the bond energy. H 2 (g) H (g) + 
18.3 Enthalpy Changes in Chemical Reactions Molecules are held together by chemical bonds. The chemical energy in a molecule is a measure of the energy.
5.4 Bond enthalpies Define the term average bond enthalpy Explain, in terms of average and enthalpies, why some reactions are exothermic and.
Topic 5.3 and 5.4 Hess’s Law and Bond Enthalpies.
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.
Exothermic and Endothermic Reactions. Energy and Chemical Reactions Chemical Energy – Energy stored in the chemical bonds of a substance. Chemical reactions.
 There is another way to calculate the heat of reaction, using bond enthalpies.  Bond enthalpy refers to the amount of energy stored in the chemical.
Chemical Equations Chapter What is a chemical reaction? We represent chemical change with a chemical reaction. Evidence that a chemical reaction.
Ch. 17 THERMOCHEMISTRY.
Exothermic and Endothermic Reactions
Bond Energy and Reactions
KEY CONCEPT Life depends on chemical reactions.
Energy and Chemical Reactions
Energy of Reactions Chemistry 11.
KEY CONCEPT Life depends on chemical reactions.
Energy & Reactions.
Heat and Endothermic and Exothermic Reactions
Can you guess the topic for today?
KEY CONCEPT Life depends on chemical reactions.
Bond Energy and Reactions
Bond Energy and Reactions
Unit 1: Reaction Kinetics
Energy Changes in Reactions (7.3)
Intro to chemistry Therm o breaking forming
KEY CONCEPT Life depends on chemical reactions.
KEY CONCEPT Life depends on chemical reactions.
Energy in Rxns & Potential Energy Diagrams
Energy Changes in Reactions
Forming New Substances
Heat and the Enthalpy of Reaction
Types of Chemical Reactions
Chemistry of Life 2.4 Chemical Reactions.
Bond Enthalpy Chem 12.
Energy Changes.
KEY CONCEPT Life depends on chemical reactions.
KEY CONCEPT Life depends on chemical reactions.
Bond Energy and Reactions
Endothermic Vs. Exothermic Reaction Graphs
Energy and Chemical Changes
Heat and the Enthalpy of Reaction
Energy Changes in Reactions
7.3 Energy Changes In Reactions
CALCULATION OF ENTHALPY CHANGE USING BOND ENERGY
KEY CONCEPT Life depends on chemical reactions.
KEY CONCEPT Life depends on chemical reactions.
This is an endothermic reaction
1.2.6 Bond Enthalpies.
Unit 1 – Reaction Kinetics Chemistry 12
14.2 Energy and Chemical Reactions
Presentation transcript:

Enthalpy of Chemical Reactions CHEMISTRY 11 Feb. 16, 2010

Chemical Bonds A molecule is composed of atoms held together by chemical bonds For a chemical reaction to occur, bonds must be broken, and new chemical bonds must form To break a chemical bond, energy must be put into molecule. (Surroundings feel cold) When chemical bonds are formed, the molecule releases energy. (Surroundings feel hot)

Chemical Bonds Every reaction contains many chemical bonds breaking and new bonds forming The total energy of a chemical reaction is the net sum of the energy released and energy absorbed by molecules A reaction is either exothermic (heat releasing) or endothermic (heat absorbing)

Enthalpy If molecules absorb heat from their surroundings, the surroundings feel cold If molecules release heat into the surroundings, the surroundings feel hot Enthalpy = “heat energy” in molecules Can only measure the change in enthalpy ∆H = H PRODUCTS - H REACTANTS

∆H > 0 Change in enthalpy is positive Products Reactants Reaction proceeding HCl H + Cl Add energy Enthalpy Changes (∆H) in Endothermic Reactions HCl + energy (kJ)  H + Cl HCl  H + Cl∆H = +energy (kJ) 431 kJ You can write change in enthalpy (∆H) in two ways:

Endothermic Chemical Reactions Endothermic reactions need more heat energy in order to start the reaction, so energy appears on the reactants side Molecules or atoms absorb energy from the surroundings, so ∆H is positive HCl kJ  H + Cl H + Cl  HCl∆H = +431 kJ

∆H < 0 Change in enthalpy is negative Products Reactants H + Cl HCl Give off energy Reaction proceeding Enthalpy Changes (∆H) in Exothermic Reactions H + Cl  HCl + energy (kJ) H + Cl  HCl∆H = -energy (kJ) 431 kJ You can write change in enthalpy (∆H) in two ways:

Exothermic Chemical Reactions Exothermic reactions produce heat energy, so energy appears on the products side Molecules or atoms lose energy to the surroundings, so ∆H is negative H + Cl  HCl kJ H + Cl  HCl∆H = -431 kJ

Change in Enthalpy in Chemical Reactions H (g) + Cl (g)  HCl (g) ∆H = -431 kJ HCl (g)  H (g) + Cl (g) ∆H = +431 kJ H 2(g) + F 2(g)  2HF (g) ∆H = -542 kJ C 2 H 5 OH (l) + 3O 2(g)  2CO 2(g) + 3H 2 O (l) ∆H = kJ

Exercises Energy & Enthalpy in Chemical Reactions Handout HEBDEN: pp , q Test February 22, 2010

Enthalpy Changes (∆H) in Chemical Reactions