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CfE Advanced Higher Chemistry Unit 1 > Reaction Feasibility > Flashcards

Flashcards in Reaction Feasibility Deck (12)
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1

What is meant by the standard enthalpy of formation, ΔHo?

The enthalpy (energy) change when one mole of a substance is formed from its elements in their standard states. Standard conditions of 1 atmosphere of pressure and temperature of 298 K

2

How can the standard enthalpy be calculated?

 

ΔHo = ΣΔHof (products) - ΣΔHo(reactants)

3

What is entropy?

The entropy (S) of a system is a measure of the degree of disorder of the system.

The greater the degree of disorder, the greater the entropy.

4

Which state of matter has the lowest disorder?

Solids have low disorder and gases have high disorder.

5

What is the relationship between entropy and temperature?

Entropy increases as temperature increases.

6

What is meant by a feasible reaction?

A reaction which always tends towards the products rather than the reactants.

7

What meant by free energy?

Free energy is the part of the total energy of a system that can do work at constant temperature and pressure.

8

How do we calculate the standard free energy change if given enthalpy and entropy?

ΔG° = ΔH° -TΔS°

9

How can the standard free energy change of a reaction be calculated from the standard free energies of formation of the reactants and products

ΔG° = ∑ΔG°f(products) - ∑ΔG°f(reactants)

10

What must ΔG° be if a reaction is to be feasible?

Negative

11

How can the temperature at which an equation becomes feasible be calculated?

T = ΔH° /ΔS°

12

If ΔH°(reaction) = - 91.8 kJ mol-1 and ΔS°(reaction) = -197.3 J K-1mol-1, calculate the temperature at which the reaction just becomes feasible.

T = ΔH° /ΔS°

T = - 91800 /- 197.3

T = 465K or 192°C