# Mass & Energy Balance Question Help

• zombieguy
In summary, the conversation discusses two questions: the first question involves calculating the flue gas composition and mass flowrate of air used when a gas with given composition is burnt with excess air. The second question involves calculating the heat addition rate in an ethanol dehydration reaction, which is an endothermic reaction. The conversation also explains the difference between endothermic and exothermic reactions and the concept of heat capacity and enthalpy change.
zombieguy
I would appretiate help with the following 2 questions, I think I've got must of the first one right (Or went off t a tangent) but I don't now where to start on the second question

1a) Calculate the flue gas composition if 100 kmol h-1 of a gas whose composition is given below are burnt with 10% excess air.
b) Calculate the mass flowrate of air used
CO-12.6%
CO2-2.6%
H2-41.6%
CH4-26.6%
O2-1.9%
N214.7%

2) Ethanol dehydration reaction is carried out in a reactor with the feed entering at 300oC
C2H5OH --> CH3CHO + H2
This is an endothermic reaction. The feed contain 90% mole % ethanol and the balance acetaldehyde. Heat is added to keep the temprature from dropping too rapidly. With a fraction of 30% and outlet temprature of 100oC.
Calculate the heat addition rate per 253 mol of the feed gas.
Below are the heat capacity data (KJ/mol-C)
Cp [C2H5OH] = 0.11
Cp [CH3CHO] = 0.08
Cp [ H2] = 0.029
Heat of reaction = 68.95 J

Take Reference Temprature = 25oCHere my Working out for question 1:
12.6CO2+6.3O2 -> 12.6CO2
41.6H2+20.8O2 -> 41.6H2O
26.6CH4+53.2O2 -> 26.6CO2+53.2H2O

Total CO2= 12.6+2.6+26.6=41.8
Total H2O=41.6+53.2=94.8
Total O2=(6.3+20.8+53.2)X1.1+1.9=90.23
Total N2=((79/21)X88.33)+14.7=346.99

After that i worked out the %'s eg. %CO2(41.8/573.82)X100=7.3% (I'd put all of my % up but I'm not sure I'm right upto this point at best)

1b) mrXmoles=mass
O2, 32X88.33=2826.56
N2, 28X332.3=9304.04
Total=12130.65

I've sorted out question 1 but I still need help with question 2.
Any help still welcome.

Help with the language used would also be helpful, thank you

Ethanol dehydration means that H2 is being removed from ethanol, which is stated in the reaction.

So, do you know the difference between an endothermic and an exothermic reaction?
One type of reaction "absorbs heat" and the other "gives off heat," which means that one type of reaction will feel cold and one will feel hot. Which one is which?

Well from the question you can gather that an endothermic reaction will "absorb heat" and so it makes the ambient cool. Every material has some ability to store heat: this is the heat capacity. Here you have been given specific heat capacities (note the units) which is the amount of heat required to raise one mole of substance one degree C. The heat of reaction is the enthalpy change that occurs during the reaction (on a molar basis).

I was planning on continuing, but I'm pretty tired.. hope this helps you.. I didn't check your work for #1 btw.

## What is mass and energy balance?

Mass and energy balance is a fundamental concept in science and engineering that involves the conservation of mass and energy in a system. It states that the total mass and energy of a closed system remains constant over time, even as it undergoes physical or chemical changes.

## Why is mass and energy balance important?

Mass and energy balance is important because it helps us understand the behavior of physical and chemical systems in nature. It is used in various fields such as thermodynamics, chemistry, and environmental science to analyze and predict the behavior of systems and processes.

## What are the key principles of mass and energy balance?

The key principles of mass and energy balance are conservation of mass and energy, mass and energy transfer, and mass and energy storage. These principles state that mass and energy cannot be created or destroyed, and they can only be transferred or stored within a system.

## How is mass and energy balance used in real-world applications?

Mass and energy balance is used in various real-world applications such as chemical reactions, power plants, and environmental systems. It is used to calculate the efficiency of a process, analyze the impact of energy usage on the environment, and design systems for optimal mass and energy transfer.

## What are the common challenges in solving mass and energy balance problems?

Some common challenges in solving mass and energy balance problems include determining the boundaries of the system, accounting for all mass and energy inputs and outputs, and dealing with complex systems that involve multiple reactions and transfers. It also requires a thorough understanding of the underlying principles and mathematical equations used in the calculations.

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