C5H12 + 8 O2 → 5 CO2 + 6 H2O
8 molecules of O2 are required.
Answer:
C. The reaction can be broken down and performed in steps
Explanation:
Hess's Law of Constant Heat Summation states that irrespective of the number of steps followed in a reaction, the total enthalpy change for the reaction is the sum of all enthalpy changes corresponding to all the steps in the overall reaction. The implication of this law is that the change of enthalpy in a chemical reaction is independent of the pathway between the initial and final states of the system.
To obtain MgO safely without exposing magnesium to flame, the reaction sequence shown in the image attached may be carried out. Since the enthalpy of the overall reaction is independent of the pathway between the initial and final states of the system, the sum of the enthalpy of each step yields the enthalpy of formation of MgO.
Answer : The exit temperature of the product is, 
Explanation :
Total heat = Heat lost by liquid + Latent heat of fusion + Heat lost by frozen

where,
Q = Total heat = 6000 kJ
m = mass of product = 15 kg
= specific heat of liquid = 
= latent heat of fusion = 
= specific heat of frozen = 
= initial temperature of liquid = 
= final temperature of liquid = 
= initial temperature of frozen = ?
= final temperature of frozen = 
Now put all the given value in the above expression, we get:
![6000kJ=[15kg\times 4kJ/kg^oC\times (10-2)^oC]+[15kg\times 275kJ/kg]+[15kg\times 2.5kJ/kg^oC\times (2-T_3)^oC]](https://tex.z-dn.net/?f=6000kJ%3D%5B15kg%5Ctimes%204kJ%2Fkg%5EoC%5Ctimes%20%2810-2%29%5EoC%5D%2B%5B15kg%5Ctimes%20275kJ%2Fkg%5D%2B%5B15kg%5Ctimes%202.5kJ%2Fkg%5EoC%5Ctimes%20%282-T_3%29%5EoC%5D)

Thus, the exit temperature of the product is, 
Answer:
2HgS + 3O2 → 2HgO + 2SO2
The coefficients are: 2, 3, 2, 2
Explanation:
HgS + O2 → HgO + SO2
The equation can be balance as follow:
Put 3 in front of O2 as shown below:
HgS + 3O2 → HgO + SO2
Now we can see that there are 6 atoms of O on the left side of the equation and a total of 3 atoms on the right side. It can be balance by putting 2 in front of HgO and SO2 as shown below:
HgS + 3O2 → 2HgO + 2SO2
Now we have 2 atoms of both Hg and S on the right side and 1atom each on the left. It can be balance by putting 2 in front of HgS as shown below:
2HgS + 3O2 → 2HgO + 2SO2
Now the equation is balanced.
The coefficients are: 2, 3, 2, 2
The law of conservation of mass(matter) states that matter(mass) can neither be created nor destroyed during a chemical reaction but changes from one form to another. An unbalanced equation suggests that matter has been created or destroyed. While a balanced equation proofs that matter can never be created but changes to different form. This is the more reason we have count the atoms of an element on both side of the equation to see if they are balanced irrespective of the new form they assume in the product