[spunkets]

"The gas in the car is chemical energy."

increasing the the kinetic E of anything, increases it's mass. Unless the speed is hugh, that extra mass is ignored.

[Lx]

I could definitely be wrong but when I took chemistry and physics a long looong time ago. We diagrammed chemical equations and everything balanced out except for a catalyst which comes through unscathed.

In physics, I'm pretty sure the teacher said that it was only a dime's worth of mass that was converted to energy in either Hiroshima or Nagasaki (the yields were reasonably close).
If I have a bowling ball at the top of a hill, it's potential energy, if I let it roll it's kinetic energy, does the bowling ball gain mass?
When it stops, does it then lose its gained mass?

Needless to say, I'm not a nuclear or chemical engineer nor a physicist and I didn't stay at a Holiday Inn last night although I did stay at a fleebag hotel next to Burbank's airport, does that count as anything?