The law of conservation of matter applies to physical changes as well as to chemical changes. if this is true, then explain why the law of conservation of matter holds true if the amount of water in a glass that was left out overnight decreases .

Because if you let it melt and there is no evaporation there will be the same amount of water.

Well, for example, when you have an ice cube(solid) and you melt it in a cup, the weight of the water after melting(liquid) will be the same as the solid.

Nothing can be created or destroyed without tampering.

The water only changed physically, turning from a liquid into a gas. 
The matter did not change at all; it only evaporated and changed its form physically.

Enchinoderms im positive

Answer:

it provides an alternative energy pathway for the reaction to proceed.

explanation:

a catalyst is a substance that speeds up the rate of a chemical reaction but is not consumed during the course of the reaction.

catalysts increase the rate of reaction without being used up. they do this by lowering the activation energy needed. with a catalyst, more collisions result in a reaction, so the rate of reaction increases. different reactions need different catalysts.

a catalyst works by providing an alternative reaction pathway to the reaction product. the rate of the reaction is increased as this alternative route has a lower activation energy than the reaction route not mediated by the catalyst.