This discussion is now closed.
Check out other Related discussions
- URGENT chem question help bond enthalpies
- enthalpy changes
- Chemistry question- enthalpy of formation
- Hess law and combustion
- Help with chemistry question please!
- energetics a level chem help!
- 2Al(s) Fe2O3(s) → Al2O3(s) 2Fe(s), struggling with this question
- Chemistry Olympiad question
- worried about my ucas appliaction?
- enthalpy change of sol more or less exo
- Chemistry ocr a level enthalpy
- enthalpy change of sol
- As level chemistry
- Enthaly Change and Hess's Law
- Chemistry question- energetics
- Help. Enthalpy question
- Enthalpy change
- Isaac physics - essential pre-uni chemistry F3.4 question help pls!!!!!!!!!!!!!!!!!!
- Hess cycle question
- Energetics Alevel chem multiple choice
Urgent -Another enthalpy question +rep
Someone please help I'm quiet stuck: *(will rep)
for both - heat capacity = 4.2 j g-1 K-1
3) When x g of calcium are added to 100cm^3 (an excess) of dilute nitric acid, the temp goes up by 11 c. The enthalpy change is 504kJmol-1. Write an equation and calulate x.
4) When 25cm^3 of 0.5 mol dm-3 magnesium chloride solution was added to 25cm^3 of potassium carbonate solution, the temp fell by 0.75 c. and a percipitate of magnesium carbonate formed. Write full and ionic equations for the reaction that occurs and calculate the enthalpy change for the reaction in kJ mol-1.
Totally lost
for both - heat capacity = 4.2 j g-1 K-1
3) When x g of calcium are added to 100cm^3 (an excess) of dilute nitric acid, the temp goes up by 11 c. The enthalpy change is 504kJmol-1. Write an equation and calulate x.
4) When 25cm^3 of 0.5 mol dm-3 magnesium chloride solution was added to 25cm^3 of potassium carbonate solution, the temp fell by 0.75 c. and a percipitate of magnesium carbonate formed. Write full and ionic equations for the reaction that occurs and calculate the enthalpy change for the reaction in kJ mol-1.
Totally lost
3) Ca + 2HNO3 --> H2 + CaNO3
Not sure about the first question. You can calculate the mass of the acid used but since there's no molarity given, you can't exactly find the number of moles of Ca(s) used and hence the mass.
4) MgCl2(aq) + K2CO3(aq) --> 2KCl(aq) + MgCO3(s)
That is basically the full equation. The ionic equation does not take into account spectator ions (ions not involved in the reaction).
You should know that KCl(aq) dissociates to K+{aq) and Cl-(aq), as do the other ions in the aqueous solutions in reactants part of the eqn.
So expanding the first reaction:
Mg2+(aq) + 2Cl-(aq) + 2K+(aq) + CO32-(aq) --> MgCO3(s) + 2K+(aq) + 2Cl-(aq)
Removing K+ and Cl- since they don't react, you get:
Mg2+(aq) + CO32-(aq) --> MgCO3(s)
This is the ionic equation.
For the next part of the question, the density of dilute acids and bases used in enthalpy calculations is always assumed to be the same as water. So m = 50g because 25ml and 25ml have been reacted together. T = 0.75C, and you know c = 4.18 J g-1 C-1.
Find H using H = mcT, and the value for H should be positive as the rxn is endothermic (temp went down).
Not sure about the first question. You can calculate the mass of the acid used but since there's no molarity given, you can't exactly find the number of moles of Ca(s) used and hence the mass.
4) MgCl2(aq) + K2CO3(aq) --> 2KCl(aq) + MgCO3(s)
That is basically the full equation. The ionic equation does not take into account spectator ions (ions not involved in the reaction).
You should know that KCl(aq) dissociates to K+{aq) and Cl-(aq), as do the other ions in the aqueous solutions in reactants part of the eqn.
So expanding the first reaction:
Mg2+(aq) + 2Cl-(aq) + 2K+(aq) + CO32-(aq) --> MgCO3(s) + 2K+(aq) + 2Cl-(aq)
Removing K+ and Cl- since they don't react, you get:
Mg2+(aq) + CO32-(aq) --> MgCO3(s)
This is the ionic equation.
For the next part of the question, the density of dilute acids and bases used in enthalpy calculations is always assumed to be the same as water. So m = 50g because 25ml and 25ml have been reacted together. T = 0.75C, and you know c = 4.18 J g-1 C-1.
Find H using H = mcT, and the value for H should be positive as the rxn is endothermic (temp went down).
Spoiler
moneyfaery
3) Ca + 2HNO3 --> H2 + CaNO3
Not sure about the first question. You can calculate the mass of the acid used but since there's no molarity given, you can't exactly find the number of moles of Ca(s) used and hence the mass.
4) MgCl2(aq) + K2CO3(aq) --> 2KCl(aq) + MgCO3(s)
That is basically the full equation. The ionic equation does not take into account spectator ions (ions not involved in the reaction).
You should know that KCl(aq) dissociates to K+{aq) and Cl-(aq), as do the other ions in the aqueous solutions in reactants part of the eqn.
So expanding the first reaction:
Mg2+(aq) + 2Cl-(aq) + 2K+(aq) + CO32-(aq) --> MgCO3(s) + 2K+(aq) + 2Cl-(aq)
Removing K+ and Cl- since they don't react, you get:
Mg2+(aq) + CO32-(aq) --> MgCO3(s)
This is the ionic equation.
For the next part of the question, the density of dilute acids and bases used in enthalpy calculations is always assumed to be the same as water. So m = 50g because 25ml and 25ml have been reacted together. T = 0.75C, and you know c = 4.18 J g-1 C-1.
Find H using H = mcT, and the value for H should be positive as the rxn is endothermic (temp went down).
Not sure about the first question. You can calculate the mass of the acid used but since there's no molarity given, you can't exactly find the number of moles of Ca(s) used and hence the mass.
4) MgCl2(aq) + K2CO3(aq) --> 2KCl(aq) + MgCO3(s)
That is basically the full equation. The ionic equation does not take into account spectator ions (ions not involved in the reaction).
You should know that KCl(aq) dissociates to K+{aq) and Cl-(aq), as do the other ions in the aqueous solutions in reactants part of the eqn.
So expanding the first reaction:
Mg2+(aq) + 2Cl-(aq) + 2K+(aq) + CO32-(aq) --> MgCO3(s) + 2K+(aq) + 2Cl-(aq)
Removing K+ and Cl- since they don't react, you get:
Mg2+(aq) + CO32-(aq) --> MgCO3(s)
This is the ionic equation.
For the next part of the question, the density of dilute acids and bases used in enthalpy calculations is always assumed to be the same as water. So m = 50g because 25ml and 25ml have been reacted together. T = 0.75C, and you know c = 4.18 J g-1 C-1.
Find H using H = mcT, and the value for H should be positive as the rxn is endothermic (temp went down).
Spoiler
hmmm thanks that helps. I learnt q=mc(Triangle)T...if q is same as H and the temperature rises then it q would be negative?
aimz08
hmmm thanks that helps. I learnt q=mc(Triangle)T...if q is same as H and the temperature rises then it q would be negative?
It's the same. And yes.
3)
Ca+2HNO3 gives Ca(NO3)2 + H2
q=mcT=100x4.2x11=4620 J
using n=enthalpy change/enthalpy change of solution
n=4620/504000
=0.00917 moles
so mass of Ca(x)=n x (relative atomic mass of Ca)
x= 0.00917 x 40.1
=0.368 g
EDIT: Enthalpy change of solution just means the enthalpy change when a solute is dissolved in a solvent,in this case Ca is dissolved in the Nitric Acid
Ca+2HNO3 gives Ca(NO3)2 + H2
q=mcT=100x4.2x11=4620 J
using n=enthalpy change/enthalpy change of solution
n=4620/504000
=0.00917 moles
so mass of Ca(x)=n x (relative atomic mass of Ca)
x= 0.00917 x 40.1
=0.368 g
EDIT: Enthalpy change of solution just means the enthalpy change when a solute is dissolved in a solvent,in this case Ca is dissolved in the Nitric Acid
thanks
SyedT
3)
Ca+2HNO3 gives Ca(NO3)2 + H2
q=mcT=100x4.2x11=4620 J
using n=enthalpy change/enthalpy change of solution
n=4620/504000
=0.00917 moles
so mass of Ca(x)=n x (relative atomic mass of Ca)
x= 0.00917 x 40.1
=0.368 g
EDIT: Enthalpy change of solution just means the enthalpy change when a solute is dissolved in a solvent,in this case Ca is dissolved in the Nitric Acid
Ca+2HNO3 gives Ca(NO3)2 + H2
q=mcT=100x4.2x11=4620 J
using n=enthalpy change/enthalpy change of solution
n=4620/504000
=0.00917 moles
so mass of Ca(x)=n x (relative atomic mass of Ca)
x= 0.00917 x 40.1
=0.368 g
EDIT: Enthalpy change of solution just means the enthalpy change when a solute is dissolved in a solvent,in this case Ca is dissolved in the Nitric Acid
aimz08
lol yeah I know - this is my first homework on enthalpy ahhh I hate chemistry and cant even drop it for A2! Dont worry others helped and now I get it well these questions anyway!
I'm the same
I'm finding chemistry so hard compared to GCSE it's unbelievable
enthalpy's the hardest thing I think I've done yet though
SyedT
No worries...you seem happy about it 
Imagine the look of horror on my face when my teacher told me that 
Imagine the look of horror on my face when my teacher told me that happy?
it was more of a sarcastic 'oh my life I am going to die' smilie, tbh
my teachers were like that too
'it'll all click by christmas'
well, christmas has come and gone...
I feel like I'll struggle through it though
just because I don't have much of a choice
hannah(:
happy?
it was more of a sarcastic 'oh my life I am going to die' smilie, tbh
my teachers were like that too
'it'll all click by christmas'
well, christmas has come and gone...
I feel like I'll struggle through it though
just because I don't have much of a choice
it was more of a sarcastic 'oh my life I am going to die' smilie, tbh
my teachers were like that too
'it'll all click by christmas'
well, christmas has come and gone...
I feel like I'll struggle through it though
just because I don't have much of a choice
I know you were being sarcastic...was just playing along
My teachers never said it'll all click together,all they said was "work hard and you'll get it". Problem is, most of the people doing chemistry don't intend to do that...
Related discussions
- URGENT chem question help bond enthalpies
- enthalpy changes
- Chemistry question- enthalpy of formation
- Hess law and combustion
- Help with chemistry question please!
- energetics a level chem help!
- 2Al(s) Fe2O3(s) → Al2O3(s) 2Fe(s), struggling with this question
- Chemistry Olympiad question
- worried about my ucas appliaction?
- enthalpy change of sol more or less exo
- Chemistry ocr a level enthalpy
- enthalpy change of sol
- As level chemistry
- Enthaly Change and Hess's Law
- Chemistry question- energetics
- Help. Enthalpy question
- Enthalpy change
- Isaac physics - essential pre-uni chemistry F3.4 question help pls!!!!!!!!!!!!!!!!!!
- Hess cycle question
- Energetics Alevel chem multiple choice
Latest
Trending
Last reply 6 days ago
Im confused about this chemistry question, why does it form these productsTrending
Last reply 6 days ago
Im confused about this chemistry question, why does it form these products
