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Ahat [919]
3 years ago
10

Under what conditions is the change in internal energy, δe rxn , equal to the heat evolved in a chemical reaction?

Chemistry
1 answer:
Stells [14]3 years ago
4 0
 the first law says that  the change in internal energy of a system is given by: 

δ<span>E = δq + δw</span>

where δ<span>E is the i change in internal energy, </span>

<span>δq is the amount of thermal energy added to the system from the surroundings </span>

<span>δw is the l work done *on* the system *by* the surroundings. </span>

<span>For a system only undergoing expansion work,
δw = -p</span>δ<span>V, so: </span>

δE = δq - p δ<span>V </span>
when δV = 0, then δe=δq
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Moles of Carbon dioxide(CO2) = 2

<h3>Further explanation</h3>

Given

Reaction

2 C2H6 (g) + 7 O2 (g) —+ 4CO2 (g) + 6 H20 (g)

Required

moles of carbon dioxide

Solution

The reaction coefficient shows the mole ratio of the compounds in the reaction equation (reactants and products)

From the equation, mol ratio of C2H6 : CO2 = 2 : 4, so mol CO2 :

mol CO2 = (4/2) x mol  C2H6

mol CO2 = 2 x 1

mol CO2 = 2

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The halpy of vaporization of H2O at 1 atm and 100 C is 2259 kJ/kg. The heat capacity of liquid water is 4.19 kJ/kg.C, and the he
Naddik [55]

Answer: Option (a) is the correct answer.

Explanation:

The given data is as follows.

        C_{p}_{liquid} = 4.19 kJ/kg ^{o}C

        C_{p}_{vaporization} = 1.9 kJ/kg ^{o}C

Heat of vaporization (\DeltaH^{o}_{vap}) at 1 atm and 100^{o}C is 2259 kJ/kg

        H^{o}_{liquid} = 0

Therefore, calculate the enthalpy of water vapor at 1 atm and 100^{o}C as follows.

            H^{o}_{vap} = H^{o}_{liquid} + \DeltaH^{o}_{vap}        

                                   = 0 + 2259 kJ/kg

                                   = 2259 kJ/kg

As the desired temperature is given 179.9^{o}C and effect of pressure is not considered. Hence, enthalpy of liquid water at 10 bar and 179.9^{o}C is calculated as follows.

             H^{D}_{liq} = H^{o}_{liquid} + C_{p}_{liquid}(T_{D} - T_{o})

                             = 0 + 4.19 kJ/kg ^{o}C \times (179.9^{o}C - 100^{o}C)

                              = 334.781 kJ/kg

Hence, enthalpy of water vapor at 10 bar and 179.9^{o}C is calculated as follows.

               H^{D}_{vap} = H^{o}_{vap} + C_{p}_{vap} \times (T_{D} - T_{o})

             H^{D}_{vap} = 2259 kJ/kg + 1.9 \times (179.9 - 100)            

                              = 2410.81 kJ/kg

Therefore, calculate the latent heat of vaporization at 10 bar and 179.9^{o}C as follows.

       \Delta H^{D}_{vap} = H^{D}_{vap} - H^{D}_{liq}              

                         = 2410.81 kJ/kg - 334.781 kJ/kg

                         = 2076.029 kJ/kg

or,                      = 2076 kJ/kg

Thus, we can conclude that at 10 bar and 179.9^{o}C latent heat of vaporization is 2076 kJ/kg.

3 0
4 years ago
You wish to make a buffer with pH 7.0. You combine 0.060 grams of acetic acid and 14.59 grams of sodium acetate and add water to
aleksandr82 [10.1K]

Answer:

The pH of the buffer is 7.0 and this pH is not useful to pH 7.0

Explanation:

The pH of a buffer is obtained by using H-H equation:

pH = pKa + log [A⁻] / [HA]

<em>Where pH is the pH of the buffer</em>

<em>The pKa of acetic acid is 4.74.</em>

<em>[A⁻] could be taken as moles of sodium acetate (14.59g * (1mol / 82g) = 0.1779 moles</em>

<em>[HA] are the moles of acetic acid (0.060g * (1mol / 60g) = 0.001moles</em>

<em />

Replacing:

pH = 4.74 + log [0.1779mol] / [0.001mol]

<em>pH = 6.99 ≈ 7.0</em>

<em />

The pH of the buffer is 7.0

But the buffer is not useful to pH = 7.0 because a buffer works between pKa±1 (For acetic acid: 3.74 - 5.74). As pH 7.0 is out of this interval,

this pH is not useful to pH 7.0

<em />

7 0
3 years ago
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