Why does hot water clean better than cold?

Answer 1

because heat kills bacteria & helps break things up easier.

Answer 2

Heat almost always makes cleaning more aggressive, in any setting.

I can think of three common behaviours that contribute to this:


1. Increased reaction rates - (kinetics)
heat speeds up all reactions, even those as humble as
water wetting it's way along the interface between some slime
and the fibre of your clothing.

2. Increased dissolving abilities - (due to entropy)
even without soap, small amounts of some greases will dissolve
in water.
In hot water, the amount that will dissolve can be ten times higher.

3. Melting -
some greases are low-melting waxes, and being melted makes it easier
for the soapy water to penetrate, detach, and surround them.
Even things that are not quite melted at least get softer.

Answer 3

The water molecules are zipping around faster - that's why the water feels hot. If you stick your hand in hot water, the H2O molecules on average are slamming into your hand at several hundreds of miles per hour. For this reason, those energetic molecules will also break up food residue on dishes faster than cold water.

Answer 4

Nix, nix on the bacteria bit -- the water is nowhere near hot enough for that, unless you are running boiling water into your washer, which I do doubt!

From AskMetaFilter:

"Unless your hot water is boiling hot, it's not going to sanitize anything. Nor is it likely to clean any better than cold water detergent in cold water. Laundry detergents intended for use with cold water dissolve at a lower water temp and have different surfactants (that's what keeps the dirt from re-depositing). Detergents intended for use in warm water won't work as well in cold water. Warm/hot water more easily dissolves powder detergents. With liquid detergents, it doesn't really matter (and most detergents, especially ones labeled for cold, are [likely] optimized for cold temperatures).

This suggests to me that increased heat may accelerate chemical reactions to get stains out or to decrease the viscocity of oils (which are really good at trapping stains).

Ah, this article backs up my notion that heat = helps dissolve oils responsible for trapping stains (and contributing to stains)."

Check out the rest of the forum thread below for more informative information, if you'd like. Hope this suffices!

Answer 5

The heat causes mollecules to move faster usually causing less viscous things to become more viscous and runny therefore making them easier to clean/wipe off. The heat can also cause expansion allowing mollecules that were stuck to become free and wiped away. The heat can also kill some bacteria.

Answer 6

Hot water breaks up chemical elements and kills the bacterial growth.

Answer 7

Helps the soap get "activated" - bubbly.