22 Enthalpy and Entropy Flashcards
Define lattice enthalpy change. (2 marks)
The enthalpy change that accompanies the formation of one mile of an ionic compound from its gaseous ions.
Define enthalpy change of atomisation. (2 marks)
The enthalpy change that occurs when the formation of one mole of gaseous atoms from the element in its standard state.
Define first electron affinity. (2 marks)
The enthalpy change that takes place when one electron is added to each atom in one mole of gaseous atoms to form one mole of gaseous 1- ions.
Why is the second electron affinity endothermic. (2 marks)
In the second one, the electron is being gained by a negative ion, this increases repulsion, so energy must be put in to force the e- onto the ion.
Describe the steps required to form a giant ionic lattice. (3 marks)
Formation of gaseous atoms
Formation of gaseous ions
Lattice formation
Define enthalpy change of formation. (2 marks)
The enthalpy charge when one mole of a compound is formed from its elements.
Define bond dissociation enthalpy. (2 marks)
The bond dissociation enthalpy is the standard enthalpy change when 1 mole of a covalent bond is broken down into two gaseous atoms.
Define first ionisation energy. (2 marks)
The enthalpy change when 1 mole of electrons is removed from 1 mole of gaseous atoms to form 1 mole of gaseous ions with a 1+ charge.
Define enthalpy change of hydration. (1 mark)
The enthalpy change when 1 mole of gaseous ions become aqueous ions.
Define standard enthalpy change of solution. (2 marks)
The enthalpy change when one mole of a solute dissolved in a solvent.
What is the equation involving specific heat capacity and mass of solution? (1 mark)
q=mc x change in T
What two enthalpy changes are used to calculate enthalpy change of solution? (2 marks)
Lattice is enthalpy change
Enthalpy of hydration
What two factors affect lattice enthalpy? (2 marks)
Ionic size
Ionic charge
What two factors affect enthalpy change of hydration? (2 marks)
Ionic size
Ionic charge
How does ionic size affect lattice enthalpy? (2 mark)
As ionic radius increases, attraction between ions decreases, so lattice enthalpy becomes less negative.
How does ionic size affect hydration enthalpy? (2 mark)
As ionic radius increases, attraction between the ions and water decreases, therefore enthalpy of hydration is less negative.
How does ionic charge affect lattice enthalpy? (2 marks)
As ionic charge increases, attraction Bert web ions increases, so lattice enthalpy becomes more negative.
How does ionic charge affect hydration enthalpy? (2 marks)
As ionic charge increases, attraction between ions and water molecules increases, so hydration energy becomes more negative.
Should a compound with endothermic enthalpy change of solution dissolve? (1 mark)
Yes
What is entropy? (2 marks)
The dispersal of energy within the chemicals making up a chemical system.
Is the entropy greater in a gas of a liquid, why? (3 marks)
Gas
The system is more random, so energy is spread out more
In a liquid, the system is less random, energy is more concentrated, so entropy is lower.
How does Mr affect entropy? (2 marks)
The higher the Mr of a substance, the higher the entropy.
Explain the effect of a higher Mr on entropy. (2 marks)
More electrons, the number of ways of arranging particles increases with the number of particles. So entropy is higher.
Explain the effect of mixing on entropy. (2 marks)
Mixing increases the entropy of a solution, because there are a greater number of ways of rearranging the particles.
Why does sodium chloride dissolve? (3 marks)
Positive changes in entropy favour chemical and physical changes.
Whilst in terms of enthalpy NaCl should not dissolve, there is a positive entropy change as the ions and water molecules mix.
What is the unit for entropy? (1 mark)
JK-1mol-1
define free energy change. (1 mark)
The overall change in energy during a chemical reaction.
What is free energy made up of? (2 marks)
Enthalpy change
Entropy change
Define enthalpy change. (2 marks)
The heat transfer between the chemical system and its surroundings.
What is the equation for free energy? (2 marks)
Free energy= enthalpy change - (temperature x entropy change)
When is the reaction feasible? (1 mark)
When free energy < 0
When is a reaction not feasible? (1 mark)
When free energy > 0
What is the value of free energy at the minimum temperature for feasibility? (1 mark)
0
