# If you leave a bottle of laundry soap in a hot car

…will the soap leak out?
Will the screw-on cap pop?

Probably okay for you car, but not so good for the detergent.

My thanks.

No.
All done.

I can tell you that, if you playfully drop a plastic bottle of detergent on your younger brother while he is lying on the floor, he will fail to see it as playful and will throw the bottle at you, missing and causing the bottle to burst on the wall spraying detergent across the room. As you frantically try to clean it up, before your mother gets back, it will soon become apparent that the task is hopeless. The more effort you put in the more suds you create. Trouble on the horizon.

Many years ago parents had a friend who went to England. She took a raincoat & a small bottle of detergent which either went into raincoat pocket or was wrapped up in raincoat (I forget all of the details). Top came off & detergent impregnated; thereafter, if she wore it in a heavy rain she would bubble down the street.

As to the OP’s question. Detergent is not under pressure so any expansion in a hot car should not cause the same issues as a can of soda could where air (CO2) could not escape until you have catastrophic container failure.

Keep in mind that detergent is transported in trucks, and non-refrigerated trucks get really hot. So it’s not likely to make any difference, anecdote notwithstanding.

If you leave a bottle of Camp Suds in the sun, it goes from green to a sort of tan or light brown. It still seems to make suds, I’m not sure if effectiveness is harmed.

Air is an “ideal gas”, which means we can express its behavior with some simple math.

Suppose the bottle is at 70F, and the pressure inside it is the same as ambient pressure (14.7) psi.

Now heat it up to 80F.

Convert the temperatures to absolute (Rankine) measurements by adding 459 to each one:

T1 = 459 + 70 = 529
T2 = 459 + 80 = 539

P2V2/T2 = P1V1/T1

Assume container volume is constant, so V2 = V1, and you can cancel them out and rearrange the Ps and Vs to get:

P2 = P1 * T2/T1

P2 = 14.7 * 539/529

P2 = 14.978 psi

Since ambient pressure is 14.7 psi, the bottle is now pressurized to (14.978 - 14.7 = ) 0.28 psi above ambient. This is the same pressure felt at the bottom of a 7.76-inch column of water. In other words, if you took your 70F bottle of detergent and turned it upside down, the cap would be experiencing roughly that much pressure. It has no problem holding that in, and probably a lot more.

The above assumes a fixed container volume, but the shape of the bottle is very likely designed so that large, flat sides can bow outward to allow the internal volume to increase under slight pressures, thereby limiting the internal pressure increase. Very likely you can leave a bottle of laundry detergent in your car in Phoenix, and although the detergent quality may suffer, you won’t make a mess of your car.

Carbonated beverages have a different problem. In addition to the pressure increase due to the warming of the gaseous CO2 above the liquid, the increased temperature decreases the solubility of the CO2 that’s dissolved in the liquid. This causes some of the CO2 to come out of solution, increasing the pressure in the can to a much greater degree then you would expect in a bottle of laundry detergent. Instead of increasing by a fraction of a PSI for a 10F increase, you might see a 10-psi increase.

https://www.chemedx.org/blog/what-pressure-inside-bottle-soda

And yes, hot cans in hot cars in hot climates can occasionally explode.

I can testify personally that this happens. And that it’s sticky.