Answer : The enthalpy change for the reaction is, 419.5 kJ
Explanation :
According to Hess’s law of constant heat summation, the heat absorbed or evolved in a given chemical equation is the same whether the process occurs in one step or several steps.
The given chemical reaction is,

Now we have to determine the enthalpy change for the reaction below:

By reversing and then dividing the reaction by 2, we get the enthalpy change for the reaction.
The expression will be:



Therefore, the enthalpy change for the reaction is, 419.5 kJ
It should just be one for it to be balanced.
Answer: B
Explanation: since the balloon is getting bigger it would make sense for the volume to increase ( get bigger) when volume increases the pressure decreases
Answer:
phosphorus.
Explanation:
The atomic number of phosphorus is 15 so the protons will be 15.
The rows are called Periods.