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What are Chemical Properties and Changes?

What are Chemical Properties and Changes?

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What are Chemical Properties and Changes?

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  1. What are Chemical Properties and Changes? • Chemical Properties:Chemical properties of matter describes its "potential" to undergo some chemical change or reaction by virtue of its composition. What elements, electrons, and bonding are present to give the potential for chemical change. It is quite difficult to define a chemical property without using the word "change". Eventually you should be able to look at the formula of a compound and state some chemical property. At this time this is very difficult to do and you are not expected to be able to do it.For example hydrogen has the potential to ignite and explode given the right conditions. This is a chemical property.Metals in general have they chemical property of reacting with an acid. Zinc reacts with hydrochloric acid to produce hydrogen gas. This is a chemical property.

  2. Chemical Changes or Reactions: • Chemical change results in one or more substances of entirely different composition from the original substances. The elements and/or compounds at the start of the reaction are rearranged into new product compounds or elements. • A CHEMICAL CHANGE alters the composition of the original matter. Different elements or compounds are present at the end of the chemical change. The atoms in compounds are rearranged to make new and different compounds. • Magnesium reacts with oxygen from the air producing an extremely bright flame. This is a chemical change since magnesium oxide has completely different properties than magnesium metal shown on the left. • The atoms are rearranged - diatomic oxygen molecules are split apart so that one oxygen atom combines with one magnesium atom.

  3. Oxidation of Iron - a chemical change: • For example iron has the potential to rust given the right conditions. This is a chemical property. • If iron does rust, this is a slow chemical change since rust is an iron oxide with different properties than iron metal. • In the graphic on the left, iron or steel wool is burning in a fast reaction with oxygen as contrasted with the slow rusting of iron also with oxygen. • In the element iron only atoms of iron are in contact with each other. In the element oxygen each oxygen is joined with one other to make a diatomic molecule. These atoms and molecules are rearranged so that two iron atoms combine with three atoms of oxygen to form a new compound.

  4. Alka Seltzer • The reactions in both of the (left and lower) cases start when a solid tablet is dropped into water. The chemicals in dry solid form must dissolve in the water before a reaction may take place. In both cases gas bubbles are observed. This is an initial chemical reaction. A flaming or glowing splint is used to test for the identity of the gases by using their chemical properties.Reactions:Alka-Seltzer: (Baking soda or sodium bicarbonate) NaHCO3 + Citric acid ---> CO2 + H2O + Sodium CitrateQUES.: Define chemical property. Then use this definition to describe the behavior toward the flaming splint for carbon dioxide in the example on the left.Answer: A chemical property defines whether a chemical reaction will or will not take place. Because the flame goes out, this shows that the chemical property of carbon dioxide gas is that no combustion reaction can take place in its presence.

  5. Efferdent • The reactions in both of the (left and upper) cases start when a solid tablet is dropped into water. The chemicals in dry solid form must dissolve in the water before a reaction may take place. In both cases gas bubbles are observed. A flaming or glowing splint is used to test for the identity of the gases. • Reaction:Efferdent: (sodium perborate - a source of hydrogen peroxide) = H2O2 + catalyst ---> O2 + H2O • QUES.: Define chemical property. Then use this definition to describe the difference in behavior toward the flaming splint for both gases in the above examples.

  6. Zinc and Iodine Reaction • The reaction in this case is between two elements, zinc metal and iodine. Both look sort of grayish in the photo. The reaction is started between the dry powders by adding a few drops of water. The reaction occurs as a combination reaction between the two elements to produce a single compound. During the reaction zinc metal gives two electrons to two iodine atoms to produce zinc +2 ions and iodide -1 ions. • The reaction is: Zn metal + I2 ----> ZnI2 • The reaction between the two elements to produce zinc iodide is very exothermic. Some of the unreacted iodine solid is heated to a gaseous iodine which is purple in color. • QUES.: A molecule is only defined as the simplest part of a compound with two or more atoms. (True or False) • QUES.: For an exothermic reaction, heat is given off in the process. (True or False) • QUES.: The fact that unreacted iodine changes to gaseous iodine is a: chemical or physical change?

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