Our laboratory plans to use one, 10-liter tank of refrigerant 134a every week. S

Question

Our laboratory plans to use one, 10-liter tank of refrigerant 134a every week. So off you go to check the cost of fill-ups at the two possible suppliers. At Chem Mart, the filled tank is returned to you at 10 bar and 90C for $10.00. At Super Discount Chemicals, they also wanted to charge you $10.00 for the fillup. You protested that the charge should be only $6.00 since they only gave you 6 bar at 0 C. You bargained and they eventually lowered the price to $8.00. You are not happy about this but decide to be scientific about the whole thing and calculate the cost/kg charged by these two suppliers. Who should you buy from? Approximate answer: one is about $1/kg, the other is about $30/kg. both the answers i get come out close to 30$/kg... I don't know how he is getting close to 1$/kg

Explanation / Answer

PV = n*R*T

1) At chem mart : n = PV/RT = 10*10 / [R * (273 + 90)] = 0.2755 / R

2) At Discount Chemicals : n = 6*10 / [R * (273 + 0)] = 0.2198 / R

Thus the cost / kg = price charged / (n*M)

1)At chem mart : (10 / 0.2755) * ( R / M) = 36.298 (R/M)

2) At Discount Chemicals: (8 / 0.2198) * (R / M) = 36.397 (R/M)

I don't know the mass of the refrigent, hence, I have expressed the answer in terms of (R/M).

Thus, it can be observed that the Chem Mart is slightly cheeper than the other. So, one should buy from Chem Mart.

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