I don't agree with Co2+ ion electronic configuration, its supposed to be 4s2 3d5 and because its a transition element, that does have variable oxidation state due to its incomplete 3d sub-shell.
I don't agree with Co2+ ion electronic configuration, its supposed to be 4s2 3d5 and because its a transition element, that does have variable oxidation state due to its incomplete 3d sub-shell.
4s is filled before 3d, and emptied before 3d as its the outermost shell, so I think the Co2+ config i put is correct
Oh I've seen something in the 1st question about Na the equation asked for the element reacting with water not the oxide of the element I think? What did everyone else write? I did 2Na + H2O ---> Na2O + H2. The other equation asked for the equation with oxide which is why I did that.
I wrote Na + H2O ---> NaOH + 1/2H2 As it didnt say it reacted with hot steam but just water so i assumed Na2O wouldnt be produced
Q8. First equation was just reacting it with 6 water moleculesP was Cr(H2O)3(OH)3Reagent was anything with OH- ions
NH3 can be used as a reagent here too!
Reagent for cr3+ to cr2+ is Zn and H+
Hydrogen fuel cell half eqn was
O2 + 4e- + 2H2O ---> 4OH- postive electrode
H2 + 2OH- ---> 2H2O + 2e- negative electrode
Overall: o2 + 2H2 ---> 2H2O
No effect if pressure increases as you are only increasing the pressure of oxygen so the same number of electron are released so same number of redox reactions??? (Not sure though)
Graph was a straight horizontal line
No effect on emf for increase in surface area of pt
Environmental advantage was h2o doesnt contribute to global warming as much as co2 and/or acid rain
Was there a question about advantage and disadvantage?? I don't remember that at aII?
The question said to calculate the standard enthalpy change for this reaction:
"The standard enthalpy of reaction (denoted ΔHr⊖) is the enthalpy change that occurs in a system when one mole of matter is transformed by a chemical reaction under standard conditions."
Maybe you're right, but my gut feeling was to divide by 2.
Chemguide had this helpful definition:
Standard enthalpy change of reaction, ΔH°r 'The standard enthalpy change of a reaction is the enthalpy change which occurs when equation quantities of materials react under standard conditions, and with everything in its standard state.'
Alevelchemistry notes say this: 'The standard enthalpy change for a reaction is the heat energy change measured under standard conditions: 100 kPa and a stated temperature (usually 298K).'
and then goes on to further clarify:
'Given a reaction: A + 3B -> 2C + 4D
The standard enthalpy change for this reaction is taken to be the enthalpy change under standard conditions when one mole of A reacts with three moles of B to give two moles of C and four moles of D.'
From this I'm now certain that dividing by 2 was not required for the marks in this question.
(It is also mentioned in these notes that it is convention to leave the answer in kJmol^-1 which means those who did divide by two to get these units have a strong case for also gaining full marks.)
I think AQA have messed up a bit there if they asked "standard enthalpy change for this reaction" Standard enthalpy change would mean dividing by 2 But the "this reaction" would suggest not However the reaction can be halved so I think the mark scheme will say that you have to divide by 2
"Standard enthalpy change of reaction, ΔH°r - The standard enthalpy change of a reaction is the enthalpy change which occurs when equation quantities of materials react under standard conditions, and with everything in its standard state."
^ The question asked for the standard enthapy change of the reaction given and you were given the correct ratio for the reaction stated, which was 2 SO2 + O2 -> 2SO3 and the standard enthalpy of formation values for these substances so you were expected to use D.H = D.H(Products) - D.H(Reactants) to work out the enthalpy change for the reaction given. The D.H calculated would give you the standard enthalpy change of such a reaction under standard conditions, which is what the question asked for.
Then you worked out the entropy change for the reaction given and put the figures into the gibbs free energy equation to work out the free energy change for the reaction given.
tl;dr: there was no reason to divide by two, if you didn't you are correct.
I think AQA have messed up a bit there if they asked "standard enthalpy change for this reaction" Standard enthalpy change would mean dividing by 2 But the "this reaction" would suggest not However the reaction can be halved so I think the mark scheme will say that you have to divide by 2
Standard enthalpy change of reaction, ΔH°r 'The standard enthalpy change of a reaction is the enthalpy change which occurs when equation quantities of materials react under standard conditions, and with everything in its standard state.'
Alevelchemistry notes say this: 'Thestandard enthalpy change for a reaction is the heat energy change measuredunder standard conditions: 100 kPa and a stated temperature (usually 298K).'
and then goes on to further clarify:
'Given a reaction: A + 3B à 2C + 4D
The standard enthalpy change for thisreaction is taken to be the enthalpy change under standard conditions when onemole of A reacts with three moles of B to give two moles of C and four moles ofD.'
From this I'm now certain that dividing by 2 was not required for the marks in this question.
(It is also mentioned in these notes that it is convention to leave the answer in kJmol^-1 which means those who did divide by two to get these units have a strong case for also gaining full marks.)
I divided by 2 and put units as kJ/mol.
Definition when I googled standard enthalpy change:
The standard enthalpy of reaction (denoted ΔHr⊖) is the enthalpy change that occurs in a system when one mole of matter is transformed by a chemical reaction under standard conditions.
For when i drew the compIex i didn't draw arrows to show co-ordinate bonds? I aIso didn't put brackets over the whoIe compIex and just put in brackets (+2 on overaII compIex) on top of the drawing. WouId i Iose marks for this??