Consider the reaction: CH_4 (g) + 2O_2 (g) rightarrow CO_2 (g) + 2H_2O (l) Delta

Question

Consider the reaction: CH_4 (g) + 2O_2 (g) rightarrow CO_2 (g) + 2H_2O (l) Delta H = -890 kJ How many grams of methane (CH_4) must be burned to produce (release) 267 kJ of heat? When 0.514 g biphenyl (C_12H_10) undergoes combustion in a bomb calorimeter, the temperature rises from 25.8 degree C to 29.4 degree C. The heat capacity of the calorimeter is 5.86 kJ/degree C. Calculate: q_rxn per mole of biphenyl for the combustion process q_rxn per gram of biphenyl for the combustion process Zinc metal reacts with hydrochloric acid according to the following balanced equation: Zn(s) + 2HCl(aq) rightarrow ZnCl_2 (aq) + H_2 (g) When 0.103 g of zinc is reacted with 50.0 g of HCl solution in a coffee-cup calorimeter, the temperature rose from 22.5 degree C to 23.7 degree C. Assume that the specific heat of the solution is the same as that of pure water, 4.18 J/g degree C. Calculate: Delta H_rxn per mol zinc for this reaction Delta H_rxn per gram of zinc for this reaction

Explanation / Answer

4.According to the reaction , CH4(g) + 2O2(g)--->CO2(g) + 2H2O, deltaH= -890 KJ

1 mole of methane releases 890 Kj of heat

1 mole of methane = 16 gm of metane ( since 16 is the molecular weight of methane)

890 Kj of heat is produced from 16 gm of CH4

267 Kj requies 267*16/890 =4.8 gm of CH4.

5. Qrxn = heat capacity of Calorimeter* temperature differene = 5.86*(29.4-25.8) =21.096 KJ

This is the heat produced per 0.514 gm, hence Qrxn per gram = 21.096/0.514=41.0428 KJ/gm

Molar mass of C12H10= 12*12+10*1= 154, moles in 0.514 gm =0.514/154= 0.003338

Qrxn/ mole = 21.096/0.003338= 6320.6 KJ/mole

6. Mass of mixture = 50+0.103 =50.103 gm

deltaH rxn= mass* specific heat* temperature difference = 50.103*4.18*(23.7-22.5)=251.32 Joules

deltaHrx/ gm = 251.32/0.103 =2440 Joules/gm

detaHrxn/moles = 251.32*63.5/0.103=158600 J/mole =158.6 Kj/mole

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