Question

In an experiment to determine the enthalpy change for this reaction, you combine 0.158 g of Mg metal with enough HCl to make 100.0 mL of solution in a coffee-cup calorimeter. The HCl is sufficiently concentrated so that the Mg completely reacts. The temperature of the solution rises from 25.6 °C to 32.8 °C as a result of the reaction. Find ΔHrxn for the reaction as written. Use 1.00 g/mL as the dens

Answer 1

The value of Δ
`H_(rxn)` for the reaction = 463
`(KJ)/(mol)`

Step-by-step explanation:

`q_(rxn) = - q_(sol)`

`q_(rxn) = H_(rxn)`

Δ
`H_(rxn)` = -
`q_(sol)` ------ (1)

We know that

`q_(sol) = m c ( T_(2) - T_(1) )`

`q_(sol) =` (1)(100) × 4.18 × (32.8 - 25.6)

`q_(sol) =` 3010 J = 3.01 Kilo Joule

From equation (1)

Δ
`H_(rxn)` = 3.01 Kilo Joule

No. of moles

`N = (m)/(M)`

m = 0.158 gm & M = 24.31 gm Mg

No. of moles

`N = (0.158)/(24.31)`

N = 0.0065

Therefore

Δ
`H_(rxn)` =
`(3.01)/(0.0065)`

Δ
`H_(rxn)` = 463
`(KJ)/(mol)`

This is the value of Δ
`H_(rxn)` for the reaction.