Thermodynamics Flashcards

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1
Q

Define Specific Heat Capacity

A

The amount of energy needed raise 1kg of a material by 1K

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2
Q

Give the equation for specific heat capacity

A

E = mcT

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3
Q

Define latent heat of vaporisation

A

The amount of energy needed to change 1kg of a material from a liquid to a gas without a rise in temperature

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4
Q

Define latent heat of fusion

A

The amount of energy needed to change 1kg of a material from a solid to a liquid without a rise in temperature

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5
Q

Give the equation for latent heat

A

E = Lm

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6
Q

Define Internal Energy

A

The internal energy of a system is the sum of the randomly distributed kinetic and potential energies of its molecules

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7
Q

Define Absolute Zero

A

The kinetic energies of molecules are zero

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8
Q

What is the link between the kinetic energy of molecules and temperature

A

Proportional as the KE increases, temperature increases

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9
Q

Dervive pV = 1/3Nmc^2

A

Consider cube of side length, l, containing molecules of mass, m.

A molecule, with velocity, u, in the x-direction. This collides during an elastic collision with the wall. This causes a change in momentum 2mu.

The time between collisions is 2l/u therefore the number of collisions per unit time is u/2l.

According to Newton’s Second Law, force is equal to the rate of change of momentum.
F = 2mu * u/2l = mu^2/l

Force on a wall is the sum of the forces of all particles:
F = m(u1^2 + u2^2+ u3^2…)/l = mN<u>/l</u>

where N is the number of molecules and <u> is mean square velocity in the x direction.</u>

Pressure is F/A. A = l^2 => mN<u>/l /l^2 = mN<u>/l^3
= mN<u>/v</u></u></u>

Overall, velocity of molecules is = <u> + +</u>

Since molecules travel uniformly in all directions. = 3<u> => 1/3 = <u></u></u>

p = mN/3V => pV = mN<u></u></u></u></u></u></u></u></u></u>

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10
Q

State the assumptions for an Ideal gas

A
Molecules are a negligible size
Molecules are identical
Collisions are perfectly elastic and the time of collisions is significantly smaller than the time between
No intermolecular forces
Molecular motion is random
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11
Q

Derive 1/2m = 3/2kT

A
pV = 1/3Nm
pV = NkT
1/3Nm = NkT
1/3m = kT
1/2m = 3/2kT

where 1/2m is the average kinetic energy of the molecules

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12
Q

Define a black body

A

An ideal body or surface that completely absorbs all radiant energy falling upon it with no reflection and that radiates at all frequencies with a spectral energy distribution dependent on its absolute temperature

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13
Q

Explains what happens with temperature on a radiation curve

A

Due to the Stefan–Boltzmann law - if you double temperature then area under graph increases by 16 (T^4)

Due to Wein’s Law the peak/max wavelength moves to the left (gets shorter) as temperature increases.

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14
Q

State the Stefan–Boltzmann law

A

L = 𝜎AT^4 where A is the surface area and T is temperature

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15
Q

State Wein’s Law

A

λmaxT = 2.9 x 10^-3

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