Final answer:
To find the mass of iron originally present when 149.9 kJ of heat was released during the formation of Fe₂O₃, we can use the equation q = mcΔT to calculate the mass.
Step-by-step explanation:
To find the mass of iron that was originally present, we can use the concept of heat transfer in a chemical reaction. The heat released in the reaction is a result of the formation of Fe₂O₃ from iron. Using the equation q = mcΔT, where q is the heat released, m is the mass of the substance, c is the specific heat capacity, and ΔT is the change in temperature, we can calculate the mass of iron.
In this case, the heat released is given as 149.9 kJ. We can assume that the reaction occurred at standard state conditions, where the temperature change (ΔT) is the difference between the final temperature of the iron and the initial temperature. Let's assume the initial temperature is 25.0°C and the final temperature is 73.3°C. The specific heat capacity of iron is 0.108 cal/g°C or 0.452 J/g°C. Rearranging the equation, we have:
q = mcΔT
149.9 kJ = m × 0.452 J/g°C × (73.3°C - 25.0°C)
Solving for m, we find:
m = 66.26 g
Therefore, the mass of the iron originally present was 66.26 g.