a) calculate the heat of reaction, in kilojoules, for the reaction:
2NO2(g) + 3H2(g)--->2NH3(g) + 2O2(g)
b) is the reaction endothermic or exothermic? how can you tell?
I will be happy to critique your work on this. You will have to look up the heats of formation.
To calculate the heat of reaction, also known as the enthalpy change (∆H), for the given reaction, you need to use the concept of Hess's Law and the heats of formation of the species involved. Here's how you can calculate it:
a) Calculate the ∆H for the given reaction:
Step 1: Write down the balanced equation with the respective stoichiometric coefficients:
2NO2(g) + 3H2(g) --> 2NH3(g) + 2O2(g)
Step 2: Look up the heats of formation (∆Hf) for each compound involved in the reaction. The heats of formation represent the enthalpy change when one mole of a substance forms from its constituent elements at standard conditions. Let's denote the heats of formation as follows:
∆Hf(NO2) = x
∆Hf(H2) = y
∆Hf(NH3) = z
∆Hf(O2) = w
Step 3: Use Hess's Law to calculate the ∆H of the reaction. Hess's Law states that the total enthalpy change of a reaction is independent of the pathway, and it can be calculated by adding the enthalpy changes of individual steps.
The enthalpy change for the reaction can be represented as:
∆H = (∆HfNH3 + 2∆HfO2) - (2∆HfNO2 + 3∆HfH2)
Substituting the ∆Hf values obtained from the heat of formation tables, you can calculate the heat of reaction in kilojoules.
b) To determine whether the reaction is endothermic or exothermic, you need to look at the sign of the ∆H value obtained in part (a). If ∆H is negative, the reaction is exothermic, meaning it releases energy to the surroundings. On the other hand, if ∆H is positive, the reaction is endothermic, indicating it absorbs energy from the surroundings.
To summarize, by using Hess's Law and the heats of formation, you can calculate the heat of reaction (∆H) for the given reaction. The sign of the obtained ∆H value will indicate whether the reaction is endothermic or exothermic.