Unit 1-Reaction Feasibility Flashcards
What is meant by the standard enthalpy of formation, ΔHof ?
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
Give a balanced equation for the enthalpy of formation of CaCO3.
Ca(s) + C(s) + 3/2O2(g) –> CaCO3(s)
How can the standard enthalpy, ΔHo be calculated?
ΔHo = ΣΔHof (products) - ΣΔHof (reactants)
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.
Which state of matter has the lowest disorder?
Solids have low disorder and gases have high disorder.
What is the relationship between entropy and temperature?
Entropy increases as temperature increases.
What is meant by a feasible reaction?
A reaction which always tends towards the products rather than the reactants.
How do we calculate the standard free energy change if given enthalpy and entropy?
ΔG° = ΔH° -TΔS°
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)
What must ΔG° be if a reaction is to be feasible?
Negative
How can the temperature at which an equation becomes feasible be calculated?
T = ΔH° /ΔS°
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
What is the second law of thermodynamics?
The total entropy of a system increases for a spontaneous process.
State the 3rd law of thermodynamics.
The entropy of a perfect crystal is zero at 0K
