Calculate the number of moles of the indicated sub- stance in each of the following samples. a. 41.5 g of mgcl2 b. 135 mg of li2o c. 1.21 kg of cr d. 62.5 g of h2so4 e. 42.7 g of c6h6 f. 135 g of h2o2

A: 0.436 moles MgCl2

B: 0.00452 moles Li2O

C: 23.3 moles Cr

D: 0.637 moles H2SO4

E: 0.547 moles C6H6

F: 3.97 moles H2O2

Explanation:

A: Calculate the number of moles of 41.5 grams of MgCl2

Molar mass of MgCl2 = 95.21 g/mol

Moles MgCl2 = 41.5 grams / 95.21 g/mol = 0.436 moles

B: Calculate the number of moles of 135 mg of Li2O

 Molar mass of Li2O = 29.88 g/mol

Moles Li2O = 0.135 grams / 29.88 g/mol = 0.00452 moles

C: Calculate the number of moles of 1.21 kg of Cr

  Molar mass of Cr = 52.0 g/mol

Moles Cr = 1210 grams / 52.0 g/mol = 23.3 moles

D: Calculate the number of moles of 62.5 grams of H2SO4

  Molar mass of H2SO4 = 98.08 g/mol

Moles H2SO4 = 62.5 grams / 98.08 g/mol = 0.637 moles

E: Calculate the number of moles of 42.7 grams of C6H6

  Molar mass of C6H6 = 78.11 g/mol

Moles C6H6 = 42.7 grams / 78.11 g/mol = 0.547 moles

F: Calculate the number of moles of 135 grams of H2O2

  Molar mass of H2O2 = 34.01 g/mol

Moles H2O2 = 135 grams / 34.01 g/mol = 3.97 moles

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the enthalpy of formation of water is given as -285.8kj/mol, which states that the enthalpy of formation is negative.

negative enthalpy of formation indicates that the heat is released during the reaction process. the heat is released from reaction to the surroundings the enthalpy is expressed with a negative sign with the energy given out in the reaction process.

the formation of water takes place by giving out heat which is -285.8 kj/mol.