2011 hsc mc q (1 Viewer)

[Chris_S]

Hey everyone sorry but I keep getting this question wrong could someone explain it to me please!

17) The molar heat of combustion of pentan-1-ol is 2800 kJ mol−1. A quantity of pentan-1-ol was combusted, generating 108 kJ of heat.
What mass of pentan-1-ol was combusted?
(A) 2.29 g
(B) 2.86 g
(C) 3.32 g
(D) 3.40 g

 

[BlueGas]

Divide 108/2800, and that'll give you moles. Then convert to mass using n = m/MM formula.

 

[kawaiipotato]

 

[Chris_S]

Thanks bluegas and kawaiipotato! Appreciate it! I just can't seem to get these calculation questions right when doing these past papers

 

[kawaiipotato]

Thanks bluegas and kawaiipotato! Appreciate it! I just can't seem to get these calculation questions right when doing these past papers

It helps to think about what you want. It asks for mass, and it gives you a relationship between moles and energy, that is, kJ/mol. Since they give you kJ, you can find mol by doing ,. that is, divide given energy by the energy/mol ratio given. Then you know the relationship between mass, molar mass and moles in order to find mass.

 

[Chris_S]

Thanks and what about this question? How did you work it out as I got the right answer by averaging the two answers and not sure if that was the right way to go or just a fluke?

20 When charcoal reacts in the presence of oxygen, carbon monoxide and carbon dioxide are produced according to the following chemical reactions.
C(s) + 1/2O2(g) → CO(g)
C(s) + O2(g) → CO2(g)
What would be the total mass of gas produced when 400 g of charcoal is reacted,
assuming equal amounts are consumed in each reaction?
(A) 0.93 kg
(B) 1.2 kg
(C) 1.5 kg
(D) 2.5 kg

 

[kawaiipotato]

20 When charcoal reacts in the presence of oxygen, carbon monoxide and carbon dioxide are produced according to the following chemical reactions.
C(s) + 1 O2(g) → CO(g) 2

Should this be 2C(s) + O2(g) --> 2CO (g)?

 

[Chris_S]

its q20 hsc 2011 paper and the 2 equations are C + 1/2O2 --> CO and C + O2 --> CO2

 

[kawaiipotato]

20 When charcoal reacts in the presence of oxygen, carbon monoxide and carbon dioxide are produced according to the following chemical reactions.
C(s) + 1 O2(g) → CO(g) 2

Was it B?

 

[Chris_S]

Yes