Types of Chemical Reactions

(See Chapter 10.4)Chemical Reactions and EnergyChemical Reactions and EnergyWhat happens when you light a match?

What happened when you mixed baking soda and strontium chloride in the lab?Chemical reactions gain or lose heat energy.EnthalpyEnthalpy amount of heat lost or gained during a chemical reaction

Symbol: H

Units: kiloJoules per mol kJ/molEnthalpyFor any chemical reaction

H = Hproducts Hreactants

Exothermic ReactionsWhat other words start with exo-?

Exothermic reaction heat out, reaction in which heat leaves (is lost)-Reaction feels hot

H < 0

Example Lighting a matchEndothermic ReactionsWhats the opposite of leaving?

Endothermic reaction heat in, reaction in which heat comes in (is gained)-Reaction feels cold

H > 0

Example Chewing gum that makes your mouth coldPracticeWhat type of reaction is:

A reaction with H = +20 kJ/mol

ExothermicEndothermic

PracticeWhat type of reaction is:

A reaction with H = -45 kJ/mol

ExothermicEndothermic

Activation Energy Diagram (Energy Graph)TermsReactant(s) The starting substance(s) in a reaction

Product(s) The substance(s) formed in a reaction

Activation energy The minimum amount of energy that particles must have in order to react = Peak H H(reactants)

ProductsReactantsActivation energyEnergy Reaction Progress Activation Energy Diagram (Energy Graph)

Label the Activation EnergyActivation EnergyActivation Energy Diagram (Energy Graph)

What is the initial energy of the reactants?100JActivation Energy Diagram (Energy Graph)

What is the activation energy of this reaction?It goes from 100J to 400 J, so 300JActivation Energy Diagram (Energy Graph)

What is the energy of the products?300JActivation Energy Diagram (Energy Graph)

The products have more/less energy than the reactants.MOREActivation Energy Diagram (Energy Graph)

Do you think this reaction released or absorbed heat?AbsorbedH = HP HR = 300 100 = +200JActivation Energy Diagram (Energy Graph)

Would you expect this reaction to feel hot or cold?Cold (absorbing heat from surroundings)Activation Energy Diagram (Energy Graph)

Is this process exothermic or endothermic?EndothermicActivation Energy Diagram (Energy Graph)Label the Activation Energy

50 100 150 200 250Activation Energy

50 100 150 200 250Activation Energy Diagram (Energy Graph)What is the initial energy of the reactants?150JActivation Energy Diagram (Energy Graph)What is the activation energy of this reaction?

50 100 150 200 250It goes from 150J to 250 J, so 100JActivation Energy Diagram (Energy Graph)What is the energy of the products?50J

50 100 150 200 250Activation Energy Diagram (Energy Graph)The products have more/less energy than the reactants.LESS

50 100 150 200 250Activation Energy Diagram (Energy Graph)Do you think this reaction released or absorbed heat?ReleasedH = HP HR = 50 150 = -100J

50 100 150 200 250Activation Energy Diagram (Energy Graph)Would you expect this reaction to feel hot or cold?Hot (Releasing heat into surroundings)

50 100 150 200 250Activation Energy Diagram (Energy Graph)Is this process exothermic or endothermic?Exothermic

50 100 150 200 250What is the total heat gain or loss of the room?

Window loses 1J of energy because it isnt sealed well.Loses 1JWhat is the total heat gain or loss of the room?

Lose 1 JHeater puts in 5 J of hot air into the room

Gains 4J

What is the total heat gain or loss of the room?

Lose 1 J

Gain 5J

Lose 1 JLose 1 JGains 2JWhat did we need to know to figure out the TOTAL heat of the room?

Gain 5J

Lose 1 J1) Amount of heat gained or lost for each item2) Total number of each itemCalculating EnthalpyStepExample1) Look up the Enthalpies of Formation (Hf) of each compound in your chemical reaction. They will be in a table.2H2(g) + O2(g) 2H2O(g)

Hf (H2) = 0 kJ/molHf (O2) = 0 kJ/molHf (H2O) = -286 kJ/mol

Calculating EnthalpyStepExample2) Multiply each Enthalpy of Formation (Hf) by the number of moles in the equation (which is the coefficient on that compound). 2H2(g) + O2(g) 2H2O(g)

Hf (H2) x 2 = 0 kJHf (O2) x 1 = 0 kJHf (H2O) x 2 = -572 kJ

Calculating EnthalpyStepExample3) Add the enthalpies of formation (Hf) of the reactants.

Then add the enthalpies of formation (Hf) of the products. 2H2(g) + O2(g) 2H2O(g)

Hf (reactants) = 0 kJ + 0 kJ = 0 kJ

Hf (products) = -572 kJ

Calculating EnthalpyStepExample4) Subtract the enthalpy of formation of the reactants from the enthalpy of formation of the products. 2H2(g) + O2(g) 2H2O(g)

H = -572 kJ 0 kJ = -572kJ

Easier to Write:H = Hf (products) Hf (reactants) Calculating EnthalpyStepExample 21)2Al(s) + 3H2O(l) Al2O3(aq) + 3H2(g)

Hf (Al) = 0 kJ/molHf (H2O) = -286 kJ/molHf (Al2O3) = -1676 kJ/molHf (H2) = 0 kJ/mol

Calculating EnthalpyStepExample 22)2Al(s) + 3H2O(l) Al2O3(aq) + 3H2(g)

Hf (Al) = 0 kJ/mol x 2 = 0kJHf (H2O) = -286 kJ/mol x 3 = -858kJHf (Al2O3) = -1676 kJ/mol x 1 = -1676kJHf (H2) = 0 kJ/mol x 3 = 0kJ

Calculating EnthalpyStepExample 23)2Al(s) + 3H2O(l) Al2O3(aq) + 3H2(g)

Hf (Al) +Hf (H2O) = -858 kJHf (Al2O3) +Hf (H2) = -1676 kJ

Calculating EnthalpyStepExample 24)2Al(s) + 3H2O(l) Al2O3(aq) + 3H2(g)

Hf (products) -Hf (reactants) = -1676kJ (-858 kJ)

H = -818kJ