Entropy

Question 1

Why should endothermic reactions not occur spontaneously

Answer 1

Because no spontaneous reactions are exothermic and reactions that are endothermic require heat from the surroundings for the reactions to occur. However some reactions which are endothermic do occur spontaneously

Question 2

I can endothermic reactions occur spontaneously?

Answer 2

There must be another factor besides the entropy change that determines whether or not a reaction can occur spontaneously. This introduces the concept of entropy.

Question 3

Spontaneous reaction

Answer 3

A reaction that happens on its own accord without any external help is called a spontaneous reaction

Question 4

Feasible / spontaneous reaction

Answer 4

This is a reactionin which ^G <0

Question 5

As disorder increases

Answer 5

Entropy increases

Question 6

Symbol and units for entropy

Answer 6

S
Jk-1mol-1

Entropy values are in J and by kJ

Question 7

Standard entropy?

Answer 7

298 k
100kpa

S•

Question 8

Simple and complex substances

Answer 8

Simple substances have low entry values, where is larger and more complex answers have much higher entropy values.

Question 9

Reactions which result in formation of gas or inc in no gaseous molecules

Answer 9

Results in an increase in entropy

Question 10

Aqueous vs solid

Answer 10

Ions and molecules in solution have higher entropiew on the corresponding solid

Question 11

Delta S

Answer 11

For all Delta S calculations, the Pirmahal in the equation must be taken into account. If two more of a reactant are use them two mol of the entropy value for the substance are used.

Question 12

Delta s pos

Answer 12

Increasing entropy i.e. increase in disorder (n.b. gas formed)

Question 13

Meg delta s

Answer 13

Decrease in entropy (NB

Question 14

How do processes lead to increased stability

Answer 14

If they lead to a lower energy state
This is obviously the situation and exothermic reaction in which the entropy (heat energy) decreases during a reaction. It therefore seems apprising that some reactions are endothermic and that these can occur spontaneously at room temperature.

Question 15

What explains if a reaction takes place

Answer 15

Entropy changes alone cannot explain this. You must consider both Delta H and Delta S

Question 16

When will a reaction be feasible

Answer 16

If delta G is less than 0

Question 17

Why if formation of magnesium oxide is highly exothermic and delta H has a high negative value it does not burn spontaneously

Answer 17

Because the reaction has a high activation energy
Magnesium and oxygen are thermodynamically on stable with respect to magnesium oxide because magnesium and oxygen are the higher energy level than magnesium oxide. The activation energy for this reaction is high therefore magnesium and oxygen are kinetically stable with respect to magnesium oxide

Question 18

Pg10

Answer 18

Oh 10

Question 19

Liquid to gas

Why positive entropy change

Answer 19

A gaseous substance is very disordered and have a much higher entropy value in the corresponding liquid.