# Using the thermochemical equation: 2NH3 (g) = 3H2 (g) + N2 (g) – 92 kJ, calculate the mass of decomposed

Using the thermochemical equation: 2NH3 (g) = 3H2 (g) + N2 (g) – 92 kJ, calculate the mass of decomposed ammonia NH3 if it is known that 276 kJ of heat was absorbed during its decomposition.

Given:
Q Art. = 92 kJ
Q1 = 276 kJ

To find:
m (NH3) -?

Decision:
1) Write the equation of the thermochemical reaction:
2NH3 (g) => 3H2 (g) + N2 (g) – 92 kJ;
2) Calculate the molar mass of NH3:
M (NH3) = Mr (NH3) = Ar (N) + Ar (H) * 3 = 17 g / mol;
3) Calculate the amount of NH3 substance, making up and solving the proportion:
If 92 kJ of heat is absorbed during the decomposition of 2 mol of NH3, then 276 kJ of heat will be absorbed during the decomposition of (x) mol of NH3:
92 kJ of heat – 2 mol NH3;
276 kJ of heat – (x) mol of NH3;
x = 276 * 2/92 = 6 mol;
n (NH3) = x = 6 mol;
4) Calculate the mass of NH3:
m (NH3) = n (NH3) * M (NH3) = 6 * 17 = 102 g.

Answer: The NH3 mass is 102 g.

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