Energy changes

Chemical changes occur when a substance combines with another to form a new substance, called chemical synthesis or, alternatively, chemical decomposition into two or more different substances. These processes are called chemical reactions and, in general, are not reversible except by further chemical reactions. Some reactions produce heat and are called exothermic reactions and others may require heat to enable the reaction to occur, which are called endothermic reactions. Understanding chemical changes is a major part of the science of chemistry. When chemical reactions occur, the atoms are rearranged and the reaction is accompanied by an energy change as new products are generated. An example of a chemical change is the reaction between sodium and water to produce sodium hydroxide and hydrogen. So much energy is released that the hydrogen gas released spontaneously burns in the air. This is an example of a chemical change because the end products are chemically different from the substances before the chemical reaction. Thinking critically 116. much discussion has focused on the need to drive more efficent cars and use less electricity.if the law of conservation of energy is true. why are people concerned about energy usage? the problem is that the original form of the energy (gasoline) is now mechanical energy and is of no use once wasteful. to make it usable again it need to be gasoline which takes an extremely long process in nature. 17. if heat flows in only one direction, how can both hot and cold liquids reach room temperature as they sit on a table? the heat from the hot object goes in the air and the air goes to the cold liquid 18. think about what happens to jack and jill in the nursery room. what kinds of enrgy are used? how was each energy form used? if they are walking they are using kinetic energy but if they are sit down they are using potential energy 19. compare the 3 temperature scales you learned about. how are they different? how are they similar? the celsius scale is based on 0°. many physical and scientific formulas can be expressed on the kelvin scale farenheit scale, water freezes at 32° and it boils at 212 ° similar: they are all based off the freezing and boiling points of water. different: they define them at different numbers. 20. use what you know about the movement of thermal energy to explain why you would place a minor burn on your arm under cool, running water. because heat is transfer from the warmer object to the cooler object.