True or False 1. Melting and evaporation involve the addition of heat: condensat

Question

True or False

1. Melting and evaporation involve the addition of heat: condensation and freezing involve the removal of heat.

2. Liquid water extinguishes a flame two ways one by absorbing much of the heat that the fire needs to sustain itself and two by wetting, which block oxygen from reaching the burning material.

3. Carbon is the only substance that can form bonds with itself indefinitely.

4. Potassium chromate changes color as its temperature changes, this is a chemical change.

5. Chemistry sets the foundation for the major earth and biological sciences.

6.Coffee and tea are decaffeinated using a fourth phase of matter known as a supercritical fluid.

Explanation / Answer

1.True.
Melting, boiling, evaporation and sublimation are the process done when heat taken in for transition of state of matter from solid to liquid, liquid to gas and solid to gas respectively.Condensation and freezing are done when heat gone out.

2.False

3.True.  Carbon can form as many as four covalent bonds and can bond to itself indefinitely. Carbon has six electrons in total, two of which are paired in an atomic orbital closest to the nucleus. The remaining four are farther from the nucleus and are available for covalent bondingThe number of possible isomers increases rapidly as the number of carbon atoms increases.

4.True.Change in color in a chromium compound is because there is a change in the oxidation state of the chromium or the number or type of ligands surrounding the chromium. These would be chemical changes involved.

5.True.

6.True. Water is more polar than caffeine is, so supercritical carbon dioxide, in the presence of a co-solvent like water, will dissolve the more non-polar substance, in this case, caffeine. In order to use supercritical carbon dioxide to decaffeinate coffee beans, the beans are first steamed until they swell (this is where the co-solvent, water, comes into play). After this, they are immersed in supercritical carbon dioxide which binds to the caffeine molecules and draws them out of the beans, leaving the coffee solids (flavor) embedded in the bean. The resulting coffee beans are about 97% caffeine free.

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