# Rocket engine operating in a vacuum

## Homework Statement

So suppose there is a chemical rocket operating in the vacuum of space (assume it's a perfect vacuum). It generates a hot gas with a total enthalpy of h. What's the final speed of the rocket exhaust, in terms of h?

## Homework Equations

The energy equation seems to be useful here:
h0 = h_exhaust + 1/2v^2 (from my textbook-- it's stated in the middle of a derivation with no explanation, but I assume it's applicable in this case)
h = c_p*T

## The Attempt at a Solution

I feel like there isn't enough information to solve the problem accurately, since we are only given h. My first thought was that because it is a perfect vacuum, we can assume the exhaust enthalpy is 0, and so v = sqrt(2*h0)

Not only does that seem too simple, but also I don't think it's reasonable that all enthalpy is lost-- wouldn't that assume T drops to absolute zero? And I thought all molecular movement stops at absolute zero, so how could there still be a flow of gas?

Can someone help me with clarifying this? Thanks!