It is a principle that states that mass cannot be loss or gained in a chemical reaction.
It happens so because,
we know that evaporation is a surface phenomenon. If surface area is increased, the rate of evaporation increases. That's why when we pour hot water in a plate it cools faster.
Answer:
Enthalpy change for the reaction is -67716 J/mol.
Explanation:
Number of moles of 
in 50.0 mL of 0.100 M of
= Number of moles of HCl in 50.0 mL of 0.100 M of HCl
= 
moles
= 0.00500 moles
According to balanced equation, 1 mol of reacts with 1 mol of HCl to form 1 mol of AgCl.
So, 0.00500 moles of react with 0.00500 moles of HCl to form 0.00500 moles of AgCl
Total volume of solution = (50.0+50.0) mL = 100.0 mL
So, mass of solution = (
) g = 100 g
Enthalpy change for the reaction = -(heat released during reaction)/(number of moles of AgCl formed)
= 
= ![\frac{-100g\times 4.18\frac{J}{g.^{0}\textrm{C}}\times [24.21-23.40]^{0}\textrm{C}}{0.00500mol}](https://tex.z-dn.net/?f=%5Cfrac%7B-100g%5Ctimes%204.18%5Cfrac%7BJ%7D%7Bg.%5E%7B0%7D%5Ctextrm%7BC%7D%7D%5Ctimes%20%5B24.21-23.40%5D%5E%7B0%7D%5Ctextrm%7BC%7D%7D%7B0.00500mol%7D)
= -67716 J/mol
[m = mass, c = specific heat capacity, 
= change in temperature and negative sign is included as it is an exothermic reaction]
1.75 (moles O2) × 6 (moles H2O) ÷ 9 (moles O2) = 1.17 (moles H2O)
You have to convert moles of O2 into moles of H2O so it's the number of moles you start with (1.75 O2) × the number of moles from the element you want (6 H20), then ÷ by the number of moles that the element that you already have (9 O2).
