study guide chem Essays

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Chemistry Midterm 2013:
1) Physical Change vs. Chemical Change:
Physical changes are limited to changes that result in a difference in display without changing the composition. Some common changes (but not limited to) are:
Change of State (Boiling Point and Melting Point are significant factors in determining this change.)
Physical properties include many other aspects of a substance. The following are (but not limited to) physical properties.
Ability to be drawn into a thin wire
Any change in these physical properties is referred to as a physical change.
Chemical changes, on the other hand, are quite different. A chemical change occurs when the substance's composition is changed. When bonds are broken and new ones are formed a chemical change occurs. The following are indicators of chemical changes:
Change in Temperature
Change in Color\
Noticeable Odor (after reaction has begun)
Formation of a Precipitate
Formation of Bubbles
Note: When two or more reactants are mixed and a change in temperature, color, etc. is noticed, a chemical reaction is probably occurring. These are not definite indicators; a chemical reaction may not be occurring. A change in color is not always a chemical change. If one were to change the color of a substance in a non-chemical reaction scenario, such as painting a car, the change is physical and not chemical. This is because the composition of the car has not changed. Proceed with caution.
1. Texture- The texture of a substance can differ with a physical change. A piece of wood was sanded, waxed, and polished; it would have a very different texture than it initially had as a rough piece of wood.
2. Color- The changing of color of a substance is not necessarily an indicator of a chemical change. Changing the color of a metal does not change its physical properties. (painting a car) However, in a chemical reaction, a color change is usually an indicator that a reaction is occurring. The guy painting the metal car is not changing the composition of the metallic substance.
3. Temperature- Although we cannot see temperature change, unless if a change of state is occurring, it is a physical change. One cannot assess this change only through visual exposure; the use of a thermometer or other instrument is necessary.
4. Shape- The shape of an object can be changed and the object will still remain true to its chemical composition. For example, if one were to fold money, the money is still chemically the same.
5. Change in sate- The change of state is likewise a physical change:
Solid→ Liquid Melting
Liquid→ Gas Vaporization
Liquid→ Solid Freezing
Gas→ Liquid Condensation
Solid→ Gas Sublimation
1. Change in temp- A change in temperature is characteristic of a chemical change. During an experiment, one could dip a thermometer into a beaker or Erlenmeyer flask to verify a temperature change. If temperature increases, as it does in most reactions, a chemical change is likely to be occurring. This is different from the physical temperature change. During a physical temperature change, one substance, such as water is being heated. However, in this case, one compound is mixed in with another, and these reactants produce a product. When the reactants are mixed, the temperature change caused by the reaction is an indicator of a chemical change.
2. Change in color- A change in color is also another characteristic of a chemical reaction taking place. For example, if one were to observe the rusting of metal over time, one would realize that the metal has changed color and turned orange. This change in color is evidence of a chemical reaction. However, one must be careful; sometimes a change in color is simply the mixing of two colors, but no real change in the composition of the substances in question.
3. Odor- When two or more