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Thermodynamics

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  1. Asked: 3 years agoIn: Thermodynamics

    Calculate the height of a column of water equivalent to atmospheric pressure of 1bar if the water is at 150C. What is the height if the water is replaced by Mercury?

    b752c
    Added an answer about 3 years ago

    Given that P = 1bar = 105N/m2 Patm = ρgh , for water equivalent105 = 1000 × 9.81 × h h = 10.19m                                                .......ANS Patm = ρgh , for Hg105 = 13.6 × 103 × 9.81 × h h = 0.749m                                              .......ANS ANS: 10.19m, 0.75m

    Given that P = 1bar = 105N/m2

     Patm = ρgh , for water equivalent

    105 = 1000 × 9.81 × h 

    h = 10.19m                                                …….ANS 

    Patm = ρgh , for Hg

    105 = 13.6 × 103 × 9.81 × h

     h = 0.749m                                              …….ANS

     ANS: 10.19m, 0.75m

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  2. Asked: 3 years agoIn: Thermodynamics

    At certain locations geothermal energy in undergound water is available and used as the energy source for a power plant. Consider a supply of saturated liquid water at 150°C. What is the maximum possible thermal efficiency of a cyclic heat engine using this source of energy with the ambient at 20°C? Would it be better to locate a source of saturated vapor at 150°C than use the saturated liquid at 150°C?  

    d279a
    Added an answer about 3 years ago

    TMAX = 150°C = 423.2 K = TH ; TMin = 20°C = 293.2 K = TL  ηTH MAX = TH - TL/TH = 130/423.2 = 0.307Yes. Saturated vapor source at 150°C would remain at 150°C as it condenses to liquid, providing a large energy supply at that temperature. 

    TMAX = 150°C = 423.2 K = TH ; TMin = 20°C = 293.2 K = TL 

     ηTH MAX = TH – TL/TH = 130/423.2 = 0.307

    Yes. Saturated vapor source at 150°C would remain at 150°C as it condenses to liquid, providing a large energy supply at that temperature. 

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  3. Asked: 3 years agoIn: Thermodynamics

    Calculate the standard reaction enthalpy for the reaction of calcite with hydrochloric acid

    CaCO3(s) + 2 HCl(aq) →

    CaCl2(aq) + H2O(ℓ) + CO2(g)

    The standard enthalpies of formation are: 

    for CaCl2(aq) : −877.1 kJ/mol; 

    for H2O(ℓ) : −285.83 kJ/mol; 

    for CO2(g) : −393.51 kJ/mol; 

    for CaCO3(s) : −1206.9 kJ/mol; and 

    for HCl(aq) : −167.16 kJ/mol.

    1. −72.7 kJ/mol 

    2. −38.2 kJ/mol 

    3. −215 kJ/mol 

    4. −116 kJ/mol 

    5. −165 kJ/mol 

    6. −15.2 kJ/mol 

     7. −98.8 kJ/mol

    4cc97
    Added an answer about 3 years ago

    Correct option (6) −15.2 kJ/molExplanation:We use Hess’ Law:∆H◦ = ∑ n ∆H◦ j,prod − ∑ n ∆H◦ j,reac= ∆H◦ f, CaCl2(aq) + ∆H◦ f, H2O(ℓ)+ ∆H◦ f,CO2(g) − [ ∆H◦ f, CaCO3(s) 2 + (∆H◦ f, HCl(aq)]= −877.1 kJ/mol + (−285.83 kJ/mol)+ (−393.51 kJ/mol) − [ −1206.9 kJ/mol + 2 (−167.16 kJ/mol)]= −15.22 kJ/mol .

    Correct option (6) −15.2 kJ/mol

    Explanation:

    We use Hess’ Law:

    ∆H◦ = ∑ n ∆H◦ j,prod − ∑ n ∆H◦ j,reac

    = ∆H◦ f, CaCl2(aq) + ∆H◦ f, H2O(ℓ)

    + ∆H◦ f,CO2(g) − [ ∆H◦ f, CaCO3(s) 2 + (∆H◦ f, HCl(aq)]

    = −877.1 kJ/mol + (−285.83 kJ/mol)

    + (−393.51 kJ/mol) − [ −1206.9 kJ/mol + 2 (−167.16 kJ/mol)]

    = −15.22 kJ/mol .

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  4. Asked: 3 years agoIn: Thermodynamics

    If the efficiency of a power plant goes up as the low temperature drops why not let the heat rejection go to a refrigerator at say –10°C instead of ambient 20°C?

    ed7da
    Added an answer about 3 years ago

    The refrigerator must pump the heat up to 20°C to reject it to the ambient. The refrigerator must then have a work input that will exactly offset the increased work output of the power plant, if they are both ideal. As we can not build ideal devices the actual refrigerator will require more work thaRead more

    The refrigerator must pump the heat up to 20°C to reject it to the ambient. The refrigerator must then have a work input that will exactly offset the increased work output of the power plant, if they are both ideal. As we can not build ideal devices the actual refrigerator will require more work than the power plant will produce extra.

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  5. Asked: 3 years agoIn: Thermodynamics

    What is the smallest temperature in degrees Fahrenheit you can have? Rankine?

    5e762
    Added an answer about 3 years ago

    The lowest temperature is absolute zero which is at zero degrees Rankine at which point the temperature in Fahrenheit is negativeTR = 0 R = −459.67 F 

    The lowest temperature is absolute zero which is at zero degrees Rankine at which point the temperature in Fahrenheit is negative

    TR = 0 R = −459.67 F 

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  6. Asked: 3 years agoIn: Thermodynamics

    State the scope of thermodynamics in thermal engineering.

    3e8d6
    Added an answer about 3 years ago

    Thermal engineering is a very important associate branch of mechanical, chemical, metallurgical, aerospace, marine, automobile, environmental, textile engineering, energy technology, process engineering of pharmaceutical, refinery, fertilizer, organic and inorganic chemical plants. Wherever there isRead more

    Thermal engineering is a very important associate branch of mechanical, chemical, metallurgical, aerospace, marine, automobile, environmental, textile engineering, energy technology, process engineering of pharmaceutical, refinery, fertilizer, organic and inorganic chemical plants. Wherever there is combustion, heating or cooling, exchange of heat for carrying out chemical reactions, conversion of heat into work for producing mechanical or electrical power; propulsion of rockets, railway engines, ships, etc., application of thermal engineering is required. Thermodynamics is the basic science of thermal engineering.

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  7. Asked: 3 years agoIn: Thermodynamics

    Define different types of properties?

    5da5a
    Added an answer about 3 years ago

    For defining any system certain parameters are needed. Properties are those observable characteristics of the system, which can be used for defining it. For example pressure, temp, volume. Properties further divided into three parts;Intensive Properties Intensive properties are those, which have samRead more

    For defining any system certain parameters are needed. Properties are those observable characteristics of the system, which can be used for defining it. For example pressure, temp, volume.

     Properties further divided into three parts;

    Intensive Properties 

    Intensive properties are those, which have same value for any part of the system or the properties that are independent of the mass of the system. EX; pressure, temp.

     Extensive Properties

     Extensive properties are those, which dependent Upon the mass of the system and do not maintain the same value for any part of the system. EX; mass, volume, energy, entropy.

     Specific Properties

     The extensive properties when estimated on the unit mass basis result in intensive property, which is also known as specific property.

     EX; sp. Heat, sp. Volume, sp. Enthalpy.

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  8. Asked: 3 years agoIn: Thermodynamics

    Convert the formula for water density in problem 21 to be for T in degrees Kelvin.

    20e64
    Added an answer about 3 years ago

    ρ = 1008 – TC/2 [kg/m3]We need to express degrees Celsius in degrees KelvinTC = TK – 273.15and substitute into formulaρ = 1008 – TC/2 = 1008 – (TK – 273.15)/2 = 1144.6 – TK/2

    ρ = 1008 – TC/2 [kg/m3]

    We need to express degrees Celsius in degrees Kelvin

    TC = TK – 273.15

    and substitute into formula

    ρ = 1008 – TC/2 = 1008 – (TK – 273.15)/2 = 1144.6 – TK/2

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  9. Asked: 3 years agoIn: Thermodynamics

    A flow of water at some velocity out of a nozzle is used to wash a car. The water then falls to the ground. What happens to the water state in terms of V, T and s? 

    4f254
    Added an answer about 3 years ago

    let us follow the water flow. It starts out with kinetic and potential energy of some magnitude at a compressed liquid state P, T. As the water splashes onto the car it looses its kinetic energy (it turns in to internal energy so T goes up by a very small amount). As it drops to the ground it then lRead more

    let us follow the water flow. It starts out with kinetic and potential energy of some magnitude at a compressed liquid state P, T. As the water splashes onto the car it looses its kinetic energy (it turns in to internal energy so T goes up by a very small amount). As it drops to the ground it then looses all the potential energy which goes into internal energy. Both of theses processes are irreversible so s goes up.

    If the water has a temperature different from the ambient then there will also be some heat transfer to or from the water which will affect both T and s. 

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  10. Asked: 3 years agoIn: Thermodynamics

    Write short notes on State, point function and path function. 

    f75b2
    Added an answer about 3 years ago

    STATE The State of a system is its condition or configuration described in sufficient detail. State is the condition of the system identified by thermodynamic properties such as pressure, volume, temperature, etc. The number of properties required to describe a system depends upon the nature of theRead more

    STATE 

    The State of a system is its condition or configuration described in sufficient detail. State is the condition of the system identified by thermodynamic properties such as pressure, volume, temperature, etc. The number of properties required to describe a system depends upon the nature of the system. However each property has a single value at each state. Each state can be represented by a point on a graph with any two properties as coordinates. 

    Any operation in which one or more of properties of a system change is called a change of state. 

    Point Function

     A point function is a single valued function that always possesses a single – value is all states. For example each of the thermodynamics properties has a single – value in equilibrium and other states. These properties are called point function or state function.

     Or

     when two properties locate a point on the graph ( coordinates axes) then those properties are called as point function.

     For example pressure, volume, temperature, entropy, enthalpy, internal energy. 

    Path Function

    Those properties, which cannot be located on a graph by a point but are given by the area or show on the graph.

    A path function is different from a point function. It depends on the nature of the process that can follow different paths between the same states. For example work, heat, heat transfer.

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