During a phase change the temperature does not change since all of the heat is being absorbed in order to break the intermolecular forces.  Due to that, the formula will not need to have T in it and is actually q=nΔH(v).
n=the number of moles (in this case 2.778mol of water since you divide 50g by 18g/mol).
ΔH(v)=the molar heat of vaporization (in this case 40.7kJ/mol).
q=the heat that must be absorbed
q=2.778mol×40.7kJ/mol
q=113.1kJ
Therefore the water needs to absorb 1.13×10²kJ.
I hope this helps.  Let me know if anything is unclear.
        
             
        
        
        
Answer:
Therefore, the rate of change in the amount of salt is 

Explanation:
Given:
Initial volume of water  lit
 lit
Flowing rate = 5 
The rate of change in the amount of salt is given by,
     ( Rate of salt enters tank - rate of sat leaves tank )
 ( Rate of salt enters tank - rate of sat leaves tank )
Since tank is initially filled with water so we write that,

Let amount of salt in the solution is  ,
,
   
    
 
Therefore, the rate of change in the amount of salt is 

 
        
             
        
        
        
Answer:
Oxygen
Explanation:
I'm not completely sure about the explosion part but I know oxygen fuels fire.
 
        
             
        
        
        
2.10
The 0 after 1 is not significant and does not affect the value of the number; therefore, when the number will be rounded to two significant figures, it will become 2.1, so it will be the same.
        
             
        
        
        
812 deciliters is the correct answer that you are looking for.