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.

the electrical  conductivity  of asolution  of an electrolyte is measured by determining the resistance of thesolution  between two flat or cylindrical electrodes separated by a fixed distance.

definition

                    entropy is a measure of the randomness or the extent of disorder of a chemical process.

                      enthalpy is a measure of the heat change of a reaction occurring at a constant pressure.

measurement units:

                        entropy is measured in joule per kelvin (jk⁻¹)   whereas enthalpy is measured in joule per mole (jmol⁻¹)

requirements:

                            entropy has no requirements or limits, and its change is measured by the division between the heat change of the chemical process and the temperature.

                              in contrast, enthalpy can only be related to the heat change of the reaction under standard conditions.