Module 13 Chemistry

A. An exothermic reaction will create _______

 

B. Is an exothermic reaction is a product or reactant?

A. Heat

B. Product

A. An endothermic reaction will produce  ________

 

B. Is an endothermic reaction a product or reactant?

A. Cold

B. reactant

Define “Change in Enthalpy” “?H”
The energy that accompanies a chemical reaction

A. ?H is positive for _________ reactions.

 

B.  ?H is negative for _________ reactions.

A. Endothermic

 

B. Exothermic

An example of enthalpy:

 

When CH4 undergoes complete combustion, the change in enthalpy of the reaction  is -803.1kJ. Where would -803,1kJ go in the chemical reaction? 

 

CH4 + 2O2 —> CO2 + 2H2O

You would include it in your reactancts since it is exothermic.

 

CH4 + 2O2 —> CO2 + 2H2O + – 803.1kJ

Use bond energies to answer this question:

 

How much energy is absorbed or released (identify which) when the following reactions takes place?

 

CH4 (g) + 2 O2 (g) –>CO2 (g) + 2 H2O (g)

 

The relevant bond energies are:

C—H 414 kJ/mol

O=O 502 kJ/mol

C=O 730 kJ/mol

O—H 464 kJ/mol

 

-656 kJ released

Know this formula:

 

ΔH = Energy required to break bonds

         – Energy released when bonds form

Study  Example 13.2 on page 425, 426, 427
State Hess’s Law
Enthalpy is a state function and is therefore independent of path.
What are standard conditions?
Most chemistry is done at room temperature of 25; Celcius and 1.00 atm

Know 13.9 formula:

;

;H; = ; ;Hf;(products) – ; ;Hf; (reactants)

Study example 13.3 on pages 432-433
Study example 13.4 on page 434-435

Study energy diagrams

;

Know how to interpret if it is an exothermic or endothermic reaction

;

Know how to figure; ;H ina diagram

Study example 13.5
Define “The Second Law of Thermodynamics”
The entropy of the universe must always either increase or remain the same. It can never decrease.
Which state of matter has the highes amount of entropy?
Gas is the highest, then liquid is second and solids are last.

A.;;Entropy of a system _________ with increasing temperature.

;

B. Entropy of a system _______ as the matter increases

A. Increases

;

B. Increases

Know formual 13.11

;

;Suniverse ; 0

Study example 13.6 on pages 442-443

Know 13.12 formula:

;

;S; = ; S; (products) – ; S; (reactants)

Know the “Gibbs Free Energy” formula (13.13)

;

;G = ;H – T*;S

;

;

Know:

;

When ;G ; 0, then the reaction is consisitent with the Second Law and is thus spontaneous.

;

When ;G ; 0, then the reaction cannot proceed, because it violates the second law

Know this formula (13.14)

;

;G; = ; ;Gf; (products) – ; ;Gf; (reactants)

Study example 13.7 on pages 448-449
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