The standard enthalpy of formation ( H f) is the enthalpy change that occurs whe

Question

The standard enthalpy of formation (Hf) is the enthalpy change that occurs when exactly 1 mol of a compound is formed from its constituent elements under standard conditions. The standard conditions are 1 atm pressure, a temperature of 25 C , and all the species present at a concentration of 1 M . A "standard enthalpies of formation table" containing Hf values might look something like this:

What is the balanced chemical equation for the reaction used to calculate Hf of SrCO3(s)?

Substance Hf H(g) 218 kJ/mol H2(g) 0 kJ/mol Sr(s) 0 kJ/mol Sr2+(aq) 549.7 kJ/mol C(g) 71 kJ/mol C(s) 0 kJ/mol N(g) 473 kJ/mol O2(g) 0 kJ/mol O(g) 249 kJ/mol S2(g) 129 kJ/mol

Explanation / Answer

to calculate the dHfo of SrC03 (s)

it should be formed from the elements in their standard state

the elemens are Sr , C and 0

the standard state of Sr is Sr (s)

the standard state of C is C (s)

and

the standard state of O is O (g)

using this info

the reaction is given by

Sr (s) + C(s) + 1.5 02 (g) ----> SrC03 (s)

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