Question

H₂ + O­₂ = H₂O

A sample of 1.22g of hydrogen is placed in the unit along with excess oxygen. The unit is initially at 22.4 C and after the reaction is complete, the finial temperature is 28.33 C. how much heat is evolved per mole of hydrogen combusted?

Answer 1

H2 + O2 = H2O

balanced

H2 + 1/2O2 = H2O

m = 1.22 g of H2

mol of H2 = mass/MW = 1.22/2 = 0.61 mol of H2

then we need 1/2 of O2 ; that is 0.61/2 = 0.305 mol of O2

mol of water formed is 1.22mol of H2O since ratio is 1:1

mass = mol*MW = 1.22*18 = 21.96 g of water

T = 22.4°C

Tf = 28.3 °C

heat evolver per mol of H2 used

first,

Q = m*Cp*dT

assume

mass = 21.96 g of water

Cp = 4.184 J/gC

dT = 28.33-22.4 = 5.93 C

Q = m*Cp*dT

Q = 21.96 *4.184 *5.93 = 544.8521 J

then

Hrxn = -Q/n

Hrxn = -544.8521/(0.61 ) = -893.20 J /mol