Question

1. Calculate the enthalpy change, ΔH, for the formation of 1 mole of strontium carbonate (the material

that gives the red color in fireworks) from its elements.

Sr(s) + C(s) + 1.5 O2(g) → SrCO3(s)

Use the following information:

2 Sr(s) + O2(g) → 2 SrO(s) ΔH = -1184 kJ

SrO(s) + CO2(g) → SrCO3(s) ΔH = -234 kJ

C(s) + O2(g) → CO2(g) ΔH = -394 kJ

2. Write chemical reactions that describe the formation of the following compounds:

a. Silver sulfate

b. Ammonium bromide

c. Tin (IV) phosphate

Answer 1

2 Sr(s) + O2(g) → 2 SrO(s) ΔH = -1184 kJ -----------------> 1

SrO(s) + CO2(g) → SrCO3(s) ΔH = -234 kJ ---------------->2

C(s) + O2(g) → CO2(g) ΔH = -394 kJ -------------------->3

equation 1 divide with 2

Sr(s) + 1/2O2(g) → SrO(s) ΔH = -592 kJ ------------> 4

addition with equation 4 and 3

Sr(s) + 1/2O2(g) → SrO(s) ΔH = -592 kJ

C(s) + O2(g) → CO2(g)          ΔH = -394 kJ

--------------------------------------------------------------

Sr(s) + C(s) +3/2O2(g) ---------. SrO(s) + CO2(g)   ΔH   = -986Kj   addition

SrO(s) + CO2(g) → SrCO3(s)                               ΔH = -234 kJ  

--------------------------------------------------------------------------------------

Sr(s) + C(s) + 3/2O2(g) --------------> SrCO3(s)       ΔH   = -1220Kj

Sr(s) + C(s) + 1.5O2(g) --------------> SrCO3(s)       ΔH   = -1220Kj

2.

a. Silver sulfate

2Ag(s) + S(s) + 2O2(g) -----------------> Ag2So4(s)

b. Ammonium bromide

    1/2N2(g) +2H2(g) + 1/2Br2(l) ---------------> NH4Br(s)

c. Tin (IV) phosphate

    3Ti(s) + P4(s) + 8O2(g)------------------> Ti3(PO4)4(s)