A2.50 g sample of powdered zinc is added to 100.0 ml of a 2.00 m aqueous solution of hydrobromic acid in a calorimeter. the total heat capacity of the calorimeter and solution is 448 j/k. the observed increase in temperature is 21.1 k at a constant pressure of one bar. calculate the standard enthalpy of reaction using these data. zn(s)+2hbr(aq)⟶znbr2(aq)+h2(g)

The standard enthalpy is -247KJ/mol.

Explanation:

The balanced equation of the reaction is :

Zn(s) + 2HBr(aq) ---> ZnBr2(aq) + H2(g)

Number of moles can be calculated by the formula:

No. of moles of zinc =

No. of moles of zinc = 0.0382 moles.

No. of moles of HBr =

No. of moles of HBr = 2.00×0.100

= 0.200

Here, the limiting reagent is Zinc because every mole of zinc used in the reaction twice of the moles of HBr are needed. HBr is present in high amounts as compared with Zinc.

Heat absorption can be calculated by:

Heat absorption= Total heat capacity × Temperature

= 448×21.1

=9452 J.

Standard enthalpy can be calculated by:

Standard enthalpy =

=

=247.

The standard enthalpy of reaction is -247 KJ/mol as the heat has been given off in the reaction.

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