Entropy

Definition of Entropy Entropy is a measure of the disorder of a substance. Low entropy: highly ordered (crystalline solid) Low entropy: low temperatures High entropy: high temperature, gases

Examples of High Entropy Gases have more entropy than liquids and solids Mixtures (solutions) more than pure substances Chemical changes that lead to more moles of products than reactants Chemical changes that produce moles of gases – especially explosions!

TNT

Why is entropy important? Processes that lead to lower energy (exothermic) are more likely to happen in our universe. Endothermic processes can also happen spontaneously if they lead to higher levels of disorder (entropy) Examples: - ice melts above 273 K - KNO3 dissolves even though the ions absorb energy from the water

Which sample has the lowest entropy? 1 mole of KNO3(l) 1 mole of KNO3(s) 1 mole of H2O(l) 1 mole of H2O(g)

In terms of energy and entropy, systems in nature tend to undergo changes toward higher energy and higher entropy higher energy and lower entropy lower energy and higher entropy lower energy and lower entropy

A reaction must be spontaneous if it is exothermic and there is an increase in entropy exothermic and there is a decrease in entropy endothermic and there is an increase in entropy endothermic and there is a decrease in entropy

Which 10-milliliter sample of water has the greatest degree of disorder? H2O(g) at 120°C H2O() at 80°C H2O() at 20°C H2O(s) at 0°C

Which list of the phases of H2O is arranged in order of increasing entropy? ice, steam, and liquid water ice, liquid water, and steam steam, liquid water, and ice steam, ice, and liquid water

Given the change of phase: CO2(g) → CO2(s) As CO2(g) changes to CO2(s), the entropy of the system decreases increases remains the same

Which process is accompanied by a decrease in entropy? boiling of water condensing of water vapor subliming of iodine melting of ice

Which of these changes produces the greatest increase in entropy? CaCO3(s) → CaO(s) + CO2(g) 2 Mg(s) + O2(g) → 2 MgO(s) H2O(g) → H2O(l) CO2(g) → CO2(s)

What is the activation energy for the catalyzed reaction in the forward direction? What is the activation energy for the uncatalyzed reaction in the reverse direction? What is the potential energy of the products?