When you add 0.401 g of sodium metal to an excess of hydrochloric acid, you find

Question

When you add 0.401 g of sodium metal to an excess of hydrochloric acid, you find that 4170 J of heat are produced. What is the enthalpy of the reaction as written below. 2Na(s) + 2 HCl (aq) ? 2NaCl(aq) + H2(g) When you add 0.401 g of sodium metal to an excess of hydrochloric acid, you find that 4170 J of heat are produced. What is the enthalpy of the reaction as written below. 2Na(s) + 2 HCl (aq) ? 2NaCl(aq) + H2(g) When you add 0.401 g of sodium metal to an excess of hydrochloric acid, you find that 4170 J of heat are produced. What is the enthalpy of the reaction as written below. 2Na(s) + 2 HCl (aq) ? 2NaCl(aq) + H2(g)

Explanation / Answer

Na moles = mass / Molar mass of Na

          = ( 0.401g) / ( 23g/mol) = 0.017435 mol

heat released per 0.017435 mol Na   = 4170 J = 4.17 KJ

heat released per 2 mol Na ( since reaction has 2Na reacted)

                                          = ( 4.17 KJ / 0.017435 mol) x 2 mol   = 478 KJ

hence enthalphy of the reaction = - 478 KJ    ( -ve sign indicates heat released)

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