physical chem flash - yellow

Question 1

What is standard enthalpy of combustion

Answer 1

Standard enthalpy of formation, H, is defined as the enthalpy change involved when one mole of a substance is formed from its elements in their standard states. Standard state of a substance is its most stable form at a pressure of 1 atom and a temp of 298k

Question 2

How can standard enthalpy of formation be used to calculate the enthalpy change for a reaction

Answer 2

Delta H= products - reactants

Question 3

What is entropy

Answer 3

Energy of a substance is a measure of the amount of disorder within that system, the larger the entropy the greater the amount of disorder. The symbol is s. Units KJ mol-1

Question 4

Solid,liquid, gas (which has highest entropy)

Answer 4

Gas highest to solid lowest

Question 5

Effect of temp on entropy

Answer 5

Higher temp means a higher degree of disorder (higher entropy) at the melting/boiling point of a substance there is a large increase in entropy

Question 6

What effect does an exothermic reaction have on the entropy of surroundings

Answer 6

Exothermic increases the entropy of surroundings as heat energy released

Question 7

What effect does an endothermic reaction have on the entropy of surroundings

Answer 7

Endothermic decreases entropy of surroundings heat energy released

Question 8

What is standard entropy of a substance

Answer 8

S, is the energy of 1 mol of the substance at temp 298K

Question 9

The entropy of a substance (perfect crystal) at 0K is zero, because particles in a solid are no longer interacting at a perfectly absorbed 0K.

Answer 9

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Question 10

What is the standard free energy change

Answer 10

A feasible reaction is a reaction that tends towards the products rather than the reactants

Question 11

What can be said about the reaction if the change in energy between reactants and products is negative

Answer 11

2nd law states that for a reaction to be feasible, total entropy for a reaction system and the surroundings must be positive for a spontaneous reaction, the total entropy and surroundings always increases

Question 12

How can degrees be converted to celsius

Answer 12

To convert degrees to kelvin, add 273

Question 13

Perfect crystal entropy at 0K is zero

Answer 13

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Question 14

Temp for a reaction to become feasible is deltah/deltas

Answer 14

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Question 15

Under non standard conditions, any reactions is a feasible one if delta g is negative

Answer 15

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Question 16

Spontaneous when delta g=0

Answer 16

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Question 17

Rate usually depends on concentration

Answer 17

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Question 18

Order of reaction can only be determined by experimental data

Answer 18

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Question 19

The rate of reaction is dependent on the slowest step called the rate determining step

Answer 19

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