Filling a Leaking Tank

ChemEStudent Material Balances Leave a Comment

A 1000ft3 tank is being filled with water at a rate of 1.04 L/min. How long (seconds) will it take to half fill the tank if there is a leak rate of 4.10 ml/s?

A) 1.07*106 s B) 2.14*106 s
C) 1.34*104 s D) 3.88*104 s
This problem can easily be solved through a mass balance on the tank. In this scenario there are no generation or consumption of the water, thus reducing the conservation of mass formula to:

Accumulation = Input - Output

This question also involves the proper conversion of units. Visit the formula tab for conversion factors.

Conservation of mass formula:
Accumulation = Input + Generation - Output - Consumption 1ft^3=28.317L


Excess Reactants

ChemEStudent General Chemistry Leave a Comment

Ammonia and Oxygen gas can be reacted together to form Nitric Oxide and Water as shown:
4NH3 + 5O2 = 4NO + 6H2O

If 100kg/day of Ammonia and 200kg/day of Oxygen gas are fed into a reactor, what is the percentage by which the excess reactant is in excess?

Use the following molecular weights:
17g/mol NH3
32g/mol O2

A) 50% B) 34%
C) 18% D) 15%
Use the molecular weight of each reactant to convert mass to moles. Using the stoichiometric relationship given by the chemical reaction, find the theoretical amount of reactant needed to complete the reaction.
To convert mass into moles: moles=mass/molecular weight
To calculate excess: excess=(fed-reacted)/fed


Understanding Dimensions Part 1

ChemEStudent General Engineering Leave a Comment

Suppose the density of a unknown fluid is given by the equation:


where ρ has units of g/L and P has units of atm. What are the units of A and B respectively?

A) g/L ; atm-1  B) g/L ; B is unitless 
C) g/L ; atm   D) A and B are unitless 



For an equation to be valid, dimensional homogeneity must exist. Also an exponent must be unitless!

There are no formulas needed to solve this question.



Concept of Entropy

ChemEStudent Thermodynamics Leave a Comment

Which of the following statements are true regarding entropy?

i) Entropy of the universe is always increasing
ii) Entropy of the system is always increasing
iii) For a reversible process, Entropy of the universe is zero
iv) Freezing liquid water would cause a decrease in the Entropy of the system
v) Entropy is a state function

A) i, ii, v  B) iii, iv, v 
C) i, iii, v  D) i, ii, iv
There are no hints for this question.
There are no necessary formulas needed for this question.