Question

The energy diagram shown represents the chemical reaction between solid ammonium chloride and solid barium hydroxide octahydrate: 2NH4Cl(s)+Ba(OH)2⋅8H2O(s)→2NH3(aq)+BaCl2(aq)+10H2O(l) The ΔH for this reaction is 54.8kJ . How much energy would be absorbed if 25.9g of NH4Cl reacts?

Answer 1

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Answer 2

the delta H for that reaction is defined by the moles of the components of the reaction. In your case that 54.8kJ of energy is needed by the reaction to convert 2 moles of NH4Cl to products.
In few words the reaction will need 54.8kJ to transform 2 moles of NH4Cl.
Now the problem wants you to calculate how much energy will be absorbed if in place of 2 moles of NH4Cl reacts only 25.9g of NH4Cl