The enthalpy of a change for the reaction of hydrogen gas with fluorine gas prod
ID: 873356 • Letter: T
Question
The enthalpy of a change for the reaction of hydrogen gas with fluorine gas produces -542 kJ.
a. what is the enthalpy per mole of hydrogen fluoride produced?
b. Is the reaction exothermic or endothermic? Explain your answer
c. Determine the Delta H for the reverse reaction, the decomposition reaction of hydrogen fluroide breaking apart into its elements and explain why.
H2 (g)---> F2 (g)---> 2HF (g) Delta H=-542 kJ
Determine the amount of energy (heat) in joules required to raise the temperature of 7.40 g of water from 29.0 degrees Celsius to 46.0 degrees celsius. Explain why this is an endothermic or exothermic process.
If the work (w) for a process is positive at contant pressure, describe what is happening to the system and the surroundings and give an example.
Explanation / Answer
1.
H2 (g) + F2 (g) ------------> 2HF(g) delta H = -542 kJ
(a) the enthalpy per mole of hydrogen fluoride produced = Enthalpy of reaction / moles of HF
the enthalpy per mole of hydrogen fluoride produced = - 542 kJ / 2 mol = - 271 kJ/mol
(b) Since delta H is -ve hence the reaction is exothermic because reaction gives out heat that's why delta H is -ve.
(c) For the reverse reaction
2HF(g) ---------> H2(g) + F2(g)
The magnitude of delta H will be same as that of forward reaction but sign will be opposite.
Hence delta H for reverse reaction = + 542 kJ
2.
Q = m_water * c_water * ( delta T)
Q = 7.4 g * 4.18 J/g degree C * ( 46 - 29) degree C
Q = 525.844 J
Q = 0.526 kJ
3.
If W is + ve then work is done on the system by the surroundings.
Considering a moving piston in a cylinder If the piston is pushed down the piston does work on the gas and we say positive work is done on the system by the surroundings.