Is humudifier putting moisture into the air a chemical or physical change?
It is a physical change.
Melting popcorn is a physical change. Because once it is melted you can allow it to harden again by leaving it out or putting it back in the fridge. If it was a chemical change you would not be able to re-solidify it. It is a physical change. You are simply changing the state of the material, as opposed to changing the compound.
a mixture is a physical reaction because, by definition, a mixture is the combination of 2 or more substances and they maintain their chemical properties. For example putting food dye in water is a mixture because although it looks like a color change (clear to colored) it is merely the dye molecules diffusing throughout the water while maintaining their chemical properties.
As you may know, determining whether a change is chemical or physical can sometimes be a real pain! This particular change is a hard one. If your talking about butter slightly melting on a hot day because it was left out on the counter, THAT is a physical change and is reversible by simply putting the butter into the fridge. However, melting butter on the stove and having it completely turn to liquid and turn…
A physical change only changes the objects apperance of an object EG; putting red food colouring in a glass of water, the water is now red, but it is still water. A chemical change changes the end product EG; lighting a peice of paper on fire it turns into ash, no matter what you do to it, it will stay ash.
Physical change does not change a substance. It could change shape - for example cutting a piece of paper in two is physical change. Putting it through a paper shredder is physical change. When ice melts, that is a physical change. So even if it changes state (solid to liquid, liquid to gas, etc), it is still a physical change. Chemical change is different. The substance has changed in a more substancial way. If you…
That's complicated. The wood is simply covered up, so that's a physical difference. Application of the paint is also physical, you are just putting it somewhere else. What happens as the paint dries depends on the type of paint. Evaporation of the solvent is also physical, but as gloss paint dries chemical changes happen to produce the permanent skin.