A-Strontium carbonate is an ionic compound that gives fireworks their red color.

Question

A-Strontium carbonate is an ionic compound that gives fireworks their red color.

Write a balanced equation for the formation of 1 mole of strontium carbonate from its elements (one of which is gaseous O2).

What is the enthalpy change (DH0) for the formation of one mole of strontium carbonate from its elements? Use the experimental results below in your calculation.

2 Sr (s) + O2 (g) -----> 2 SrO (s)                          DH0rxn = -1184 kJ

SrCO3 (s) ---->SrO (s) + CO2 (g)                      DH0rxn = +234 kJ

C(s) + O2 (g) ----->CO2 (g)                                  DH0rxn = -394 kJ

Explanation / Answer

a)

Find entropy formation of SrCO3

2 Sr (s) + 2C(s) + 3O2 (g) ----->2SrCO3 (s)

b)

2 Sr (s) + O2 (g) -----> 2 SrO (s)                          DH0rxn = -1184 kJ

SrCO3 (s) ---->SrO (s) + CO2 (g)                      DH0rxn = +234 kJ

C(s) + O2 (g) ----->CO2 (g)                                  DH0rxn = -394 kJ

Eqn 2, must be inverted

2 Sr (s) + O2 (g) -----> 2 SrO (s)                          DH0rxn = -1184 kJ

SrO (s) + CO2 (g) ---->SrCO3 (s) DH0rxn = -234 kJ

C(s) + O2 (g) ----->CO2 (g)                                  DH0rxn = -394 kJ

Multipy eqn 2 and 3 by 2

2 Sr (s) + O2 (g) -----> 2 SrO (s)                          DH0rxn = -1184 kJ

2SrO (s) + 2CO2 (g)   ---->2SrCO3 (s) DH0rxn = -468 kJ

2C(s) + 2O2 (g) ----->2CO2 (g)                                  DH0rxn = -788 kJ

Add all equations

2 Sr (s) + O2 (g) + 2SrO (s) + 2CO2 (g) +2C(s) + 2O2 (g) -----> 2 SrO (s) + 2SrCO3 (s) +2CO2 (g)

Eliminate common terms

2 Sr (s) + 2C(s) + 3O2 (g) ----->2SrCO3 (s) dH = -1184 kJ -468 kJ -788 kJ = -2440

dHrxn = -2440 kJ

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