Q1.The table below shows data for the four hydrocarbons ethyne, propyne, propene and propane. AHc is the standard enthalpy of combustion of these hydrocarbons.
Compound
Name
M
-AHC
/kJ mol
HCECH
ethyne
26
1300
HC-CCH,
propyne
40
1940
H. C=CHCH,
propene
42
2060
CH, CH, CH
propane
44
2220
The complete combustion of 2.0 g of one of the above hydrocarbons releases exactly 100 kJ of
heat energy
This hydrocarbon is
A
ethyne
B
propyne
C
propene
D
propane
(Total 1 mark)

Explanation:

It often helps to write the heat as if it were a reactant or a product in the thermochemical equation.

Then you can consider it to be "moles" of "kJ"  

We will need a chemical equation with masses and molar masses, so, let's gather all the information in one place.

M_r:               26

              2H-C≡C-H + … ⟶   1300 kJ + …

m/g:              2.0

1. Moles of HC≡CH

2. Heat released

The molar ratio is 1300 kJ:1 mol HC≡CH

c. heat could easily travel through the molecules in the air and escape/enter the flask. removing the air slows down the heat transfer.