Question

Which of the following displays the correct change in enthalpy and best describes the reaction below? 2CsCl(aq) + Na2SO4(aq) 2NaCl(aq) + Cs2SO4(aq) Given: Cs2SO4: ∆H= -1400 kJ CsCl: ∆H= -415 kJ Na2SO4: ∆H= -1380 kJ NaCl: ∆H = -411 kJ
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Answer 1

We subtract the enthalpies of the reactants from that of the products:
$2\Delta H(NaCl)+\Delta H(Cs_2 SO_4)-2\Delta H(CsCl)-\Delta H(Na_2 SO_4) \\ =2(-411)+(-1400) -2(-415)-(-1380) \\ = -12 kJ$
Since this is < 0, this is an exothermic reaction.