Multiple Choice
If you have 3.2 grams of Zn, how many liters of H2 gas could be produced in the following chemical reaction at STP? Zn(s) + 2 HCl(aq) → ZnCl2(aq) + H2(g)
3. Chemical Reactions
Stoichiometry
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Stoichiometric amounts of nitrogen gas and hydrogen gas react in a calorimeter to produce 5 g of ammonia gas. The calorimeter temperature rises 0.42 °C. The calorimeter and water have a combined heat capacity of 32.16 kJ/°C. Calculate the heat of formation of ammonia (in kJ/mol).
A
-91.8 kJ/mol
B
-45.9 kJ/mol
C
-183.6 kJ/mol
D
-136.2 kJ/mol
Verified step by step guidance1
Identify the chemical reaction: Nitrogen gas (N₂) reacts with hydrogen gas (H₂) to form ammonia (NH₃). The balanced chemical equation is: N₂(g) + 3H₂(g) → 2NH₃(g).
Calculate the heat absorbed by the calorimeter using the formula: q = C × ΔT, where q is the heat absorbed, C is the heat capacity of the calorimeter, and ΔT is the change in temperature. Here, C = 32.16 kJ/°C and ΔT = 0.42 °C.
Determine the moles of ammonia produced using its molar mass. The molar mass of NH₃ is approximately 17.03 g/mol. Use the formula: moles of NH₃ = mass of NH₃ / molar mass of NH₃.
Calculate the heat of formation per mole of ammonia. Since the reaction produces 5 g of ammonia, use the heat absorbed by the calorimeter and the moles of ammonia to find the heat of formation: ΔH_f = q / moles of NH₃.
Compare the calculated heat of formation with the given options to identify the correct answer.
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