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CHEM103 Lecture Notes - Lecture 2: Nonmetal, Chlorine, Solubility

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27 Mar 2018

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University of Delaware

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Chemistry and Biochemistry

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A chemical change is one in which bonds are broken or formed. Atoms rearrange and the structures of molecules are changed. Since chemical bonds store energy, chemical reactions can consume or release energy. 4 al(s) + 3 o 2 (g) 2 al 2 o 3 (s) 4 al atoms + 3 o 2 molecules react to give 2 molecules (units) of al 2 o 3. 4 moles of al + 3 moles of o 2 react to give 2 moles of al 2 o 3. An is used to show the conversion from reactants (consumed) to products (produced) For reversible reactions, a double arrow is used. The amount of each particle is shown with a number in front of the particle, called a stoichiometric coefficient. Stoichiometric coefficients show the number of that type of particle, counted either as particles or moles. The letters: s, l, g, and aq show the physical state of the substance.

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Related Questions

Stoichiometric Equalities

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Atoms can bond to other atoms to make molecules. Atoms sometimes break these bonds and form them in a different way. For example, it is possible to take two molecules of hydrogen (H_2) and one molecule of oxygen (O_2), put them near one another, give them a little spark to help them start a reaction, and you will end up with two molecules of water (H_2O). Do you see what happened? Some of the H-H bonds and the O-O bonds broke and were replaced by O-H bonds. The process of forming or breaking bonds is called a chemical reaction. Chemical reactions come in a vast variety of types. But they typically involve energy changes that are, very roughly, 5 times 10^-19 J per molecule. We can use that number to estimate some useful quantities. Be sure to write your units in the answers below. Gasoline is made up of molecules with carbon and hydrogen (C and H). There are many kinds of molecules in a typical gasoline; but let's assume that all of them are in the form of C_8H_17. That substance has a mass of 18 times 10^-26 kg per molecule. If the mass density of gasoline is 720 kg/m^3, then how many molecules are in one gallon of gasoline? (1 m^3 = 264 gallons.) Please show your work and don't just look it up on the web. Here's a keep track of your units. At the end, the units should cancel out and your answer for the number of molecules should have no units. When you burn gasoline, you convert chemical energy to heat or work (to make your car move). If, when you burn gasoline, you convert 5 times 10^-19 J per molecule, how much energy can be obtained from one gallon of gasoline? If your car has a mass of 1,000 kg, then how much energy is needed to make your car go from rest to 65 mph (29 m/s)? (Think of this using kinetic energy. Ignore friction with the air or road.) How many gallons of gasoline are needed to make your car go from rest to 65 mph (29 m/s). (This is a rough estimate, neglecting the energy lost to air friction, heat, and other things.) If gasoline costs $2.20 per gallon, how much money does your answer to part (d) cost ?