Differentiate physical change from chemical change?
What are the two kinds of mixtures? Define each.
What are solutions?
Answer:
Chemical changes are the changes in a substance through chemical reactions. The chemical reactants form a new product with equal mass.
The following evidence can indicate that a chemical change took place, although this evidence is not conclusive:
Change in color (e.g., rusting of iron causes a change in color from silver to reddish-brown).
Change in temperature or energy, such as the production (exothermic) or loss (endothermic) of heat.
Change of form (burning paper) (this change is difficult to reverse).
An unexpected change in color
Light, heat, or sound is given off.
Gases formed, often appearing as bubbles.
Formation of precipitate (chunks).
For example, placing a pot of water on a hot stove element causes a change in temperature and a gas to be released (water vapor) but a chemical change did not take place.
A chemical reaction produces new substances by changing the way in which atoms are arranged. In a chemical reaction old bonds are broken and new bonds are formed between different atoms. This breaking and forming of bonds takes place when particles of the original materials collide with one another.
A physical change involves the change in a substance that does not involve a chemical reaction, as opposed to a chemical change. Since no reaction occurs, there are no chemical substances present after a physical change that were not there before the change. Because of this, a physical change is often said to be reversible. However, this definition is sometimes misleading, as many physical changes are difficult to reverse (such as cutting paper) and some chemical reactions reverse very easily .
Another way in which the distinction between chemical and physical changes is often expressed is to state that only chemical reactions involve the rearrangement of atoms. Again, this distinction may again be misleading because cutting a piece of paper is a rearrangement of atoms.
Examples of physical change include:
Change of state (such as solid to liquid)
Creation or separation of a mixture (including homogeneous mixtures, where the solute may not be visible)
Physical deformation (cutting, denting, stretching, etc.)
Change in color by addition of dye
Some expanded examples:
If a piece of paper is cut up into small pieces it still is paper. This is a physical change in the shape and size of the paper. If the same piece of paper is burned, it is broken up into different substances that are not paper, and thus burning is a chemical reaction. (Paper itself is a mixture of substances.)
If one decided to mix sugar into water to make sugar water, this would be a physical change as the water could be evaporated and sugar crystals would reappear. However, if one baked a cake with flour, water, sugar and other ingredients, new substances would appear. It would take extraordinary means to return the various ingredients out to their original form. Chemical reactions occur in the baking process, and the changes are chemical changes.
The answers post by the user, for information only, FunQA.com does not guarantee the right.
More Questions and Answers: