Given that cao(s) + h2o(l) → ca(oh)2(s), δh°rxn = –64.8 kj/mol, how many grams of cao must react in order to liberate 525 kj of heat?

454.3 g.

Explanation:

1.0 mol of CaO liberates → – 64.8 kJ.

??? mol of CaO liberates → - 525  kJ.

∴ The no. of moles needed = (1.0 mol)(- 525 kJ)/(- 64.8 kJ) = 8.1 mol.

∴ The no. of grams of CaO needed = no. of moles x molar mass = (8.1 mol)(56.077 g/mol) = 454.3 g.

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