A particular reactant decomposes with a half‑life of 103 s when its initial concentration is 0.349 M. The same reactant decomposes with a half‑life of 215 s when its initial concentration is 0.167 M

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explanation:

- lead + phosphoric acid = hydrogen + lead(ii) phosphate

1. for the first question, we must find the mass of the anhydrous salt, mgso₄. the molar mass for mgso₄·7h₂o is 246.47 g/mol, while that of mgso₄ is 120.37 g/mol.7.834 g mgso₄·7h₂o * 1 mol mgso₄·7h₂o/246.47 g * 1 mol mgso₄/1 mol mgso₄·7h₂o * 20.37 g mgso₄/mol = 0.647 g mgso₄

2. mass of water = mass of sample - mass of anhydrous salemass of water = 7.834 - 0.647 = 7.19 gpercent water in hydrate = 7.19/7.834 * 100 = 91.74%

your answer is a. the enthalpy of formation for a pure element in its standard state is always positive.