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Can anyone tell me what these two equations represent?

Physics Asked by Dio on April 11, 2021

I’ve just seen these without any explanation of what the variables are or what are do they describe, I just know it should be something about convex lenses and starting fire with them.

$$Q_r=C^n(-Delta H_r)Ze^{-frac{E}{RT}}$$

I’m not sure if the triangle represents delta as change or if it’s a Laplace operator

$$C_prhofrac{partial T}{partial t}=Q_r-Q_c$$

Can anyone tell me what the variables are and what do these equations represent?

One Answer

What is the source?

Broadly, the first is an Arrhenius equation, which provides the rate of a thermally activated process, i.e., one with an activation energy.

$Q_r$: a rate (based on the second equation, likely a heat flux)
$C^n$: some type of pre-exponential factor, where n may be the reaction order; problem specific
$-Delta H_r$: H often stands for enthalpy and r for reaction
$Z$: typically a collision frequency
$E$: the activation energy
$R$: the gas constant
$T$: the temperature

The second equation is a heat capacity equation describing how an object heats up from a net heat flux.

$C_p$: specific heat capacity at constant pressure
$rho$: density
$t$: time
$Q_r$: likely an input heat flux, with units of J/m³s
$Q_c$: likely an output heat flux, perhaps to a cold sink (c)

Put together, the equations provide an energy balance: the thermal energy generated from a reaction minus any output thermal energy goes into heating the system.

Correct answer by Chemomechanics on April 11, 2021

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