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Balancing Equations

Hello , I have recently done to mock papers for my chemistry exam and on both exams I had questions involving balancing equations but with diatomic molecules in them .

Q1. NaBr = Na + Br ?
I thought the equation was already balanced but apparently the correct answer was
A. 2Nabr = 2Na + Br2
- I thought this was due to Br being a diatomic molecule..

Q2. CaCl2 = Ca + Cl?
I thought that once again the question was already balanced because Cl is a diatomic molecule .. so there should be the same amount on both sides.. but the answer was
A. CaCl2 = Ca + 2Cl

Please help me understand how this has happened? whats really confusing me is that in the first question, even without the subscript there you still count the Br as Br2 but in the second question it expected me to put a coefficient 2 there..
Original post by OliverHartless
Hello , I have recently done to mock papers for my chemistry exam and on both exams I had questions involving balancing equations but with diatomic molecules in them .

Q1. NaBr = Na + Br ?
I thought the equation was already balanced but apparently the correct answer was
A. 2Nabr = 2Na + Br2
- I thought this was due to Br being a diatomic molecule..

Q2. CaCl2 = Ca + Cl?
I thought that once again the question was already balanced because Cl is a diatomic molecule .. so there should be the same amount on both sides.. but the answer was
A. CaCl2 = Ca + 2Cl

Please help me understand how this has happened? whats really confusing me is that in the first question, even without the subscript there you still count the Br as Br2 but in the second question it expected me to put a coefficient 2 there..


The suggested answer on question 2 is incorrect. Chlorine is diatomic and so it should be:

Ca + Cl2 --> CaCl2
Original post by charco
The suggested answer on question 2 is incorrect. Chlorine is diatomic and so it should be:

Ca + Cl2 --> CaCl2


Does this mean the equation was already balanced in the first case? all I had to do was just put the subscript 2 in place?
Original post by OliverHartless
Does this mean the equation was already balanced in the first case? all I had to do was just put the subscript 2 in place?


The equation was not officially 'balanced' it was incorrect. You cannot balance an incorrect equation.
Original post by charco
The equation was not officially 'balanced' it was incorrect. You cannot balance an incorrect equation.


Ok thankyou but just to clarify .. The exam question was
Q. The metal calcium can be extracted by the electrolysis of molten calcium chloride. please balance the incomplete equation below.
CaCl2 --> Ca + Cl

What would be the correct thing for me to write to that?
Reply 5
Original post by OliverHartless
Ok thankyou but just to clarify .. The exam question was
Q. The metal calcium can be extracted by the electrolysis of molten calcium chloride. please balance the incomplete equation below.
CaCl2 --> Ca + Cl

What would be the correct thing for me to write to that?


I would say CaCl2 ----> Ca + 2Cl,

But what charco was saying is correct. Since chlorine is a diatomic molecule it comes as
'Cl2'.
(edited 9 years ago)
Reply 6
I agree with Reety



Posted from TSR Mobile
The equation for the electrolysis of molten calcium chloride is CaCl2 --> Ca + Cl2
Looks like an error on the mark scheme. If the question answer are in a textbook this is highly likely as they are often full of errors but errors even happen on exam mark schemes! :eek:

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