Module 5 Chapter 22
No description yet. This curated deck is ready for daily study.
Card preview (24)
What are features of ionic compounds
They are very stable with high melting points
What are ionic bonds
They are the strong electrostatic forces of attraction between oppositely - charged ions in the ionic lattice structure
What is a feature of the energy that is required to break the lattice
There is a substantial energy barrier that has to be broken down in the lattice
What is lattice enthalpy
A measure of the strength of ionic bonding in a giant ionic lattice
What is lattice enthalpy
The enthalpy change due to the formation of 1mol of ionic lattice from gaseous ions (under standard conditions)
What are features of lattice enthalpy
It provides a measure of ionic bonding strength -It is always exothermic
What is the standard enthalpy change of atomisation
It is the enthalpy change of forming 1mol of gaseous atoms from the element in its standard state under standard conditions
What is a feature of standard enthalpy change of atomisation
It is always endothermic
What is a feature of the standard enthalpy change of atomisation
If the elements is a gas this value is related to bond enthalpy
What is first electron affinity
Is the enthalpy change when an electron is added to each atom in 1mol of gaseous atoms of -1 gaseous ions
What is a feature of first electron affinity
It is always exothermic Successive electron affinities are needed for greater charges
Why are successive electron affinities endothermic
As the electron is repelled by the negative ion
What is a feature of measuring lattice enthalpy
Lattice enthalpy can’t be measured directly, must be calculated - indirectly using known enthalpy changes in an energy cycle
What is the standard enthalpy change of solution
It is the enthalpy change due to 1 mole of a solute dissolving in a solvent
What is a feature of the enthalpy change of solution
It can be exothermic or endothermic
What is the enthalpy change of hydration
It is the enthalpy change due to dissolving gaseous ions in water to form 1 mole of aqueous ions
How the the enthalpy change of solution be calculated experimentally
BY recording the temperature change when adding an ionic compound to water
What is the method for working out the enthalpy change of solution
• Take the mass of one of the salts • Measure 50cm^3 of distilled water and add to a polystyrene cup and take its temperature • Add the salt to water and stir with the thermometer • Record the greatest temperature change
What is the equation to calculate the enthalpy change of solution
Mass x specific heat capacity x change in temperature/ 1000 x moles
What is the mass in the equation
It is the mass of the solute + the mass of the solvent
What happens when an ionic compound dissolves
The ionic lattice breaks to form separate ions —> therefore is opposite change from lattice enthalpy The gaseous ions are attracted tot the polar water to become hydrated aqueous ions —> energy change = enthalpy change of hydration
How can you categorise whether the enthalpy change of solution is exothermic or endothermic
If the lattice enthalpy change is greater than the enthalpy change of hydration - endothermic If the lattice enthalpy change is less than the enthalpy change of hydration - exothermic
What determines whether an ionic compound is soluble or insoluble
The relative magnitude of lattice and hydration enthalpies helps to explain this variety.
What do lattice enthalpy values depend on
ionic size and ionic charge