Propane gas (C3H8) enters a home furnace at 25oC, 1 atm, and burns completely with 15% excess dry air also entering at 25oC, 1 atm. The combustion products at 167 oC, 1 atm exit through the chimney after passing over the air heating coil. Air from the house enters the coil at 17oC, 1 atm, with a volumetric flow rate of 30m3 /min and heated air is discharged into the heating ducts at 50oC, 1 atm. There is no significant stray heat loss from the outside of the furnace, and kinetic and potential energy effects can be neglected. If propane gas costs $10 per 1000 m3 , determine the total seasonal fuel cost based on 2160 h of operation.

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the answer is the first option

explanation:

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answer : third trial had the contaminated sample and the correct value for dhrxn should be 1000 kj/mol

explanation :

let us write down the given equations

equation 1 :

equation 2 :

equation 3 :

let us use hess's law to find out which 2 equations can be added to get the third equation.

let us reverse equation 2 and multiply it by 2. the new equation that we get is,

equation 4 :

let us add equation 1 & 4

the above equation is similar to equation 3 but has different value for dhrxn.

therefore third trial had the contaminated sample and the correct value for dhrxn should be 1000 kj/mol