Oceans - Unit 8 Flashcards
Describe arrangement of NaCl?
Each Na surrounded by 6 Cl and each Cl is surrounded by 6 Na
What determines the solubility of ionic lattices?
- Sub with large lattice enthalpies are insoluble
What type of process is the dissolving of ions?
Endothermic ( as bond breaking endo)
Ions in sol then hydrated in exothermic process (as bond making exo)
Define lattice enthalpy?
The enthalpy change when one moles of solid is formed by the coming together of the separate ions
Will the lattice enthalpy be positive or negative?
Always exo
Will the enthalpy change of hydration be positive or negative?
Always exo
Will the enthalpy change of solution be positive of negative?
Exo or endo
What determines the size of the lattice enthalpy?
Stronger ionic attractions = large lattice enthalpy
What makes lattice enthalpies more negative?
Higher charge density of ion:
Higher charge - means ions attract each other more strongly
Smaller radius - ions can come closer together
Attractions between ions and water molecules?
ion-dipole interactions
What does it mean for ions to be hydrated?
They have water mols bound to them
What determines how hydrated an ion is?
How strong it’s bonds are with the water mol.
How many water mols should you should surrounding one ion?
4
Define enthalpy change of hyrdation?
The enthalpy change for the formation of a solution of ions from one mol of gaseous ions
How does the charge density affect enthalpy change of hydration?
Larger charge density = More exothermic
More charged = attract water mols more strongly
Smaller = Get closer to water mols
therefore, greater attraction between ions and water mols
What is the enthalpy change of solution?
The enthalpy change when one mole of a solute dissolves to form a very dilute sol.
What is the solubility when the enthalpy change of sol. is negative?
solute normally dissolve
What is the solubility when the enthalpy change of sol. is positive?
solute doesn’t insoluble
Solubility of ionic lattice in non-polar solvents (hexane)?
No soluble
the mols in solvent not charged so unable to interact with ions
Describe global warming?
1 - UV + Visible light radiation from sun hits earth, heating it
2 - This is re-emitted by earth as IR
3 - This IR is absorbed by greenhouse gases causing vibrations of bonds within mols
4 - These gases then transmit vibrational E to neighboring mols
5 - Some IR remitted to earth, heating it
6 - Causes global warming
What happens to the Infared energy once it’s absorbed by greenhouse gases?
1 - Increase vibrational E of molecules so bonds vibrate more.
- The vibrational E can then be transferred to other mols by collisions
- This increases mols KE, increasing T of air
2 - Some infrared emitted to earth or into space
What is the IR window?
The wave length of infrared radiation that water vapour does not absorb
How does water vapour regulate earth’s temp?
1 - Less infrared radiation absorbed
2 - More emitted to space
issue with Co2?
1 - Absorbs infrared at same WL as the IR window
- Therefore infrared radiation that would have passed through atmosphere now absorbed
2 - CO2 raises temps
- therefore more water vapour
- therefore more radiation absorbed
What is the Bronsted Lowry theory of acids and bases?
Acids proton donors
Bases proton acceptors
Conjugate acid-base pair?
Conjugate base = ion of an acid that acts as a base + accepts H+ to form the acid
Conjugate acid = acid formed from this
How can the position of an equilibrium tell you about the strength of an acid?
further to right = stronger acid
What buffer?
A solution which resists a change in pH for small additions of acid/alkali
How do buffers work?
1 - Weak acid reacts with OH-, preventing sol. becoming more alkaline
2 - Salt reacts with H+, preventing sol. becoming more acidic
What is a buffer sol. made of?
Weak acid + it’s salt
Weak base + it’s salt
=What are the two assumptions made in order to describe how a buffer works?
Assumption 1: - All A- ions come from salt - The Weak acid, HA, supplies very few A- compared to salt Assumption 2: - Almost All HA remains unchanged
Why is a weak acid and a salt needed in a buffer sol?
weak acid - acts as source of H+
salt - acts as a sink for H+ ions
What happens when alkali added?
1 - Alkali removes H+
2 - H+ regenerated from HA
3 - pH re-established
What do the conc. of the acid and alkali need to be in buffer?
Similar, so can equally resist addition of acid/alkali
How does water effect buffer?
1 - conc. of acid and salt equally reduced therefore ph not effected
What kind of gas is CO2?
Acidic
What is Ksp?
- Constant which describes the solubility of a product
- The solubility product
Two outcomes regarding Ksp when ions are mixed together?
- The value of the ions concentration multiplied is greater than Ksp = then compound will precipitate out of sol
- The value is less/equal to Ksp = ions will remain in sol (are soluble)
What is entropy?
A measure of the number of ways of arranging molecules and distributing energy
When is entropy change positive vs negative?
Positive = products more disordered than reactants (e.g solid --> gas) (therefore products have higher entropy than reactants) Negative = reactants more disordered than products (e.g gas --> solid)
How does state of a substance link to the entropy?
Gases + more complex mols = highest entropy
Liquids = 2nd highest
Solids + Giant covalent/lattice = Lowest entropy
Units of entropy?
JK-1mol-1
What is the chemical system?
products and reactants
What increases entropy change of system?
Increasing temp
Entropy of mixture compared to two separate things?
1 - entropy mixture higher
