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3 years ago

Write an equation that expresses the law of thermodynamics in terms of heat and work

Chemistry

1 answer:

Anettt [7]3 years ago

3 0

We write DE = q+w, where DE is the internal energy change and q and w are heat and work, respectively.

(b)Under what conditions will the quantities q and w be negative numbers?

q is negative when heat flows from the system to the surroundings, and w is negative when the system does work on the surroundings.

As an aside: In applying the first law, do we need to measure the internal energy of a system? Explain.

The absolute internal energy of a system cannot be measured, at least in any practical sense. The internal energy encompasses the kinetic energy of all moving particles in the system, including subatomic particles, as well as the electrostatic potential energies between all these particles. We can measure the change in internal energy (DE) as the result of a chemical or physical change, but we cannot determine the absolute internal energy of either the initial or the final state. The first law allows us to calculate the change in internal energy during a transformation by calculating the heat and work exchanged between the system and its surroundings.

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Lana71 [14]

Answer:

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Explanation:

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3 years ago

Consider the reaction: 2 H2O (g)-->2 H2 (g) + O2 (g). ΔH=483.6 Kj/mol. If 2 moles of H2O (g) are converted H2(g) and O2(g) ag

denis-greek [22]

DE = dH - PdV

2 H2O(g) → 2 H2(g) + O2(g) 

You can see that there are 2 moles of gas in the reactants and 3 moles of gas in the products. 

1 moles of ideal gas occupies the same volume as 1 mole of any other ideal gas under the same conditions of temp and pressure. 

Since it is done under constant temp and pressure that means the volume change will be equal to the volume of 1 mole of gas 

2 moles reacts to form 3 moles 

The gas equation is 

PV = nRT 
P = pressure 
V = volume (unknown) 
n = moles (1) 
R = gas constant = 8.314 J K^-1 mol^-1 
- the gas constant is different for different units of temp and pressure (see wikki link) in this case temp and pressure are constant, and we want to put the result in an equation that has Joules in it, so we select 8.314 JK^-1mol^-1) 
T = temp in Kelvin (kelvin = deg C + 273.15 
So T = 403.15 K 

Now, you can see that PV is on one side of the equation, and we are looking to put PdV in our dE equation. So we can say 

dE = dH -dnRT (because PV = nRT) 

Also, since the gas constant is in the unit of Joules, we need to convert dH to Joules 

dH = 483.6 kJ/mol = 483600 Joules/mol 

dE = 483600 J/mol - (1.0 mol x 8.314 J mol^-1K-1 x 403.15 K) 
dE = 483600 J/mol - 3351.77 J 
dE = 480248.23 J/mol 
dE = 480.2 kJ/mol

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3 years ago

Read 2 more answers

The energy required to split apart dichlorine according to the equation is 3.99 × 10-19 J/molecule. Cl2(g) → 2Cl(g) Calculate th

Natasha2012 [34]

Answer:

The frequency of the photon that can dissociate dichlorine is 6.02×10¹⁴ Hz

Explanation:

The energy of a photon is given by the equation:

E=h·f

E=3.99×10⁻¹⁹ J/molecule

h (Planck's constant)=6.626×10⁻³⁴ m²·kg/s

∴ f=E/h

$f=\frac{3.99*10^{-19}J}{6.626*10^{-34} m²·kg/s}$ =6.02×10¹⁴ s⁻¹= 6.02×10¹⁴ Hz

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Answer:

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Answer:

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