Other standard enthalpy changes

There are possibly as many standard enthalpy changes as there are types of reactions. Some common ones other than those mentioned in previous articles include:

1. Standard enthalpy of hydrating an anhydrous salt (not to be confused with standard enthalpy of hydration), e.g.

$CuSO_4(s)+5H_2O(l)\rightarrow CuSO_4\cdot 5H_2O(s)\; \; \; \; \; \; \; \Delta H_{hydt}^{\: o}=-78.2\: kJmol^{-1}$

1. Standard enthalpy of precipitation, e.g.

$AgNO_3(aq)+NaCl(aq)\rightarrow AgCl(s)+NaNO_3(aq)\; \; \; \; \; \Delta H_{ppt}^{\: o}=-65.8\; kJmol^{-1}$

Question

Calculate the enthalpy of precipitation of PbBr₂ when 150.0 mL of 0.500 M Pb(NO₃)₂is added to 80.0 mL of 1.000 M NaBr in a calorimeter with the temperature rising from 298.15 K to 299.28 K (assuming that the solution’s specific heat capacity is 4.200 Jg^-1K^-1 and its density is 1.0 g/ml).

Answer

0.0800 moles of NaBr precipitates 0.0400 moles of PbBr₂. Using eq5 from a basic level article,

$\Delta H_{ppt}=-(4.200)(150.0+80.0)(299.28-298.15)=-1092\: J$

$\Delta H_{ppt}=\frac{-1092}{0.0400}=-27.3\: kJmol^{-1}$

Other standard enthalpy changes

Question

Answer

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