unit 1b: reaction feasibility

Question 1

thermochemistry

Answer 1

the study of energy changes that take place during chemical reactions

Question 2

energy changes can be used to predict

Answer 2

the feasibility of a reaction i.e. whether it will spontaneously take place

Question 3

standard enthalpy of formation

Answer 3

the enthalpy change when one mole of a substance is formed from its elements in their standard states

Question 4

standard state of a substance

Answer 4

its most stable state at standard conditions

Question 5

standard conditions

Answer 5

298K (room temp=25degreesC)

Question 6

standard enthalpy of formation for an element

Answer 6

zero (as there is no enthalpy change involved)

Question 7

a spontaneous/feasible reaction

Answer 7

one which happens of its own accord (doesn’t need energy input)

Question 8

spontaneous reactions tend towards…

Answer 8

the products rather than reactants

Question 9

example of a spontaneous/feasible reaction

Answer 9

rusting

Question 10

entropy

Answer 10

a measure of the degree of disorder in a system, the greater the entropy, the greater the disorder

Question 11

state and entropy values

Answer 11

solids have low disorder and gases high disorder, changes of state involve large changes in entropy

Question 12

an example of perfect entropy and zero disorder

Answer 12

a crystal lattice at absolute zero (0K)

Question 13

temperature and entropy values

Answer 13

entropy increases and temperature increases

Question 14

the second law of thermodynamics

Answer 14

the total entropy of a reaction system and its surroundings always increases for a spontaneous/feasible reaction

Question 15

exothermic reactions (negative deltaH)

Answer 15

increases the entropy of the surroundings

Question 16

endothermic reactions (positive deltaH)

Answer 16

decreases the entropy of the surroundings

Question 17

the standard entropy of a substance

Answer 17

the entropy value for the substance in its standard state

Question 18

units for entropy

Answer 18

JK^-1mol^-1

Question 19

deltaG represents

Answer 19

the energy available ‘to do work’- the excess energy available beyond that needed just to make the reaction spontaneous

Question 20

for a reaction to be feasible

Answer 20

deltaG must be negative

Question 21

deltaG=0

Answer 21

reaction is just feasible/ at equilibrium

Question 22

when deltaS is negative

Answer 22

the reaction is exothermic

Question 23

deltaHf°

Answer 23

the standard enthalpy of formation

Question 24

deltaS

Answer 24

entropy

Question 25

deltaS must be positivite for

Answer 25

a spontaneous reaction

Question 26

deltaS°

Answer 26

standard entropy change

Question 27

deltaG

Answer 27

free energy