Kinetics Entropy Lesson Crash Course Chemistry – Entropy 2:35-

Thermodynamics - the study of the relationship of heat and other energy forms that accompany all physical and chemical changes in matter. (Provides no information about the rate or speed of reactions)  

Spontaneous Processes - proceeds on its own without any outside intervention. Examples: ice melting at rm temp cooling of a hot object water flowing down hill soda fizzing when opened radioactive decay iron rusting

Spontaneous processes are driven by a tendency to reach a state of minimum potential energy because low potential energy represents a stable situation.   Most spontaneous processes are exothermic

ΔH = Hproducts - Hreactants Enthalpy - refers to the transfer of energy ΔH = Hproducts - Hreactants

Endothermic Reaction (+ΔH) Hreactants < Hproducts PEreactants < PEproducts  

Exothermic Reaction (-ΔH) Hreactants > Hproducts PEreactants > PEproducts  

Are the reverse reactions of the examples above also spontaneous?   No, the reverse process generally require an expenditure of more energy.

- a quantitative measure of the disorder,  Entropy (S) - a quantitative measure of the disorder, or randomness in the substances in a reaction.      Solid Liquid Gas

Entropy when gases are formed from liquids and solids. CO2(s) → CO2(g) H2O(l) → H2O(g)   increases

Entropy (S) 2nd Law of Thermodynamics – Entropy – Words/Letters Chemistry An Atoms Focused Approach Chap 12 - Entropy

Entropy when solutions are formed from liquids and solids. NaCl(s) → Na+(aq) + Cl-(aq)   increases H2O

Entropy when there are more molecules of gas as products than there are as reactants. 2NH3(g) → N2(g) + 3H2(g) NH4Cl(s) → NH3(g) + HCl(g)   increases

Entropy when the temperature of a substance is increased. H2O(l, 25◦C) → H2O(l, 50 ◦C)   increases

Thermodynamic Law - states that in any spontaneous process, the overall entropy of the universe always   There is a strong tendency for things to become increases. more disordered.

The entropy of the surroundings increases or decreases because of the heat transfer by a reaction   An exothermic reaction (-ΔH) heats up the surroundings, increasing the entropy of the surroundings An endothermic reaction (+ΔH) cools the surroundings, decreasing the entropy of the surroundings

Entropy (S) The Mixing of Ideal Gases    The Mixing of Ideal Gases For our example, we shall again consider a simple system of two ideal gases, A and B, with a number of moles nA and nB, at a certain constant temperature and pressure in volumes of VA and VB, as shown in Figure 1. These two gases are separated by a partition so they are each sequestered in their respective volumes. If we now remove the partition (like opening a window in the example above), we expect the two gases to randomly diffuse and form a homogenous mixture as we see in Figure 2.