CHE 106 Lecture Notes - Lecture 6: Tricalcium Phosphate, Arsenic Trioxide, Adenosine A2B Receptor

Science Tutor: Chemistry Name: Mixtures, Solutions, &Compounds: Chemical Equations Date Chemical Equations If a chemical symbol can be thought of as a letter and a chemical formula as a word in the language of chemistry, then a chemical equation is a statement or sentence. A chemical equation is a shorthand way of describing a chemical reaction between two or more substances. A "+ sign means "combines with." An arrow points away from the reactants and toward the products (See page 10), and an arrow means "yields." 2Na + Cl2 → 2NaCl means sodium combines with chlorine to yield sodiumn chloride (salt) Look closely at the equation above. Notice the "2" in front of NaCI on the right and Na on the left. That 2, called a coefficient, is necessary to make this equation balance. Remember Antoine Lavoisier? (Page 15) Matter is neither created nor destroyed in a chemical reaction. The same number of each kind of atom must be on both sides of a chemical equation. Because chlorine only exists as a molecule consisting of two chlorine atoms, it requires two atoms of sodium to yield two molecules of salt (NaCI). This illustrates another important law stated clearly by the French chemist Joseph-Louis Proust in 1799. Chemical compounds always combine in certain specific fixed proportions. Wherever sodium and chlorine combine, two atoms of sodium will be necessary to react with one molecule of gaseous chlorine. 1 . For the equation 2Mg + O2→ 2MgO + energy: A. List the reactant or reactants 2Hato B. List the product or products C. How many atoms of magnesium does it take to combine with one molecule of oxygen? D. How many molecules of magnesium oxide are produced in this reaction? 2. Hydrogen can combine with oxygen to produce water. We could write the equation like this: H2 + O2 → H2O. But this equation is unbalanced! Rewrite this equation with the correct coefficients so that an atom of oxygen doesn't disappear! (Be careful. If you add a coefficient to one side you may have to adjust the other. Count all the atoms.) 3. Now that you have the idea, balance the following equations: A, Pho, → PbO + 02 C. Ca + H2O → Ca(OH)2 + H2 How is following a recipe to mix up a batch of biscuits (or any other food item) similar to Proust's law for chemical reactions? 4. OMark Twain Media, Inc., Publishers 17

Balance the following equations. Mgo SF. Hao HF CO, 6. Recall the stoichiometric coefficients (the numbers before the individual species) in a balanced chemical reaction refer to the number of moles of that species involved in the chemical reaction. A balanced chemical equation shows the molar relationship between all of the reactants and products. Now, given the following chemical equaton: 3 Cu 8 HNO, 3 cu(NO, 2 NO 4 Hao a. Is this equation balanced? Yes/No) b. How many moles of HNO, are required to react with 6 moles of Cu? c. How many moles of cu(NO,,are produced when 3 moles of Cu react? d. How many moles of Cu must react to produce 4 moles of NO? e. If 4 moles of No are produced, how many moles of H,0 are also produced? 7. Propane. CH. is commonly used as a fuel in gas grills. n reacts with oxygen according to 3 CO2 4 Hzo C, H. 5 O How many grams of propane can be burned by 24 g of o,? 8. Lead (l) oxide, Pbo, reacts with ammonia, NH, as follows: 3 Pbo 2 NH 3, Pb Na 3 Hzo How many grams of Pb are formed when 0,105 g NH, react? 9. Lithium hydroxide absorbs carbon dioxide forming lithium carbonate and water. 2 LioH CO2 Lico, Halo If a reaction vessel contains 0.15 moles of LioH and 0.08 moles Co, which compound is the limiting reagent?

A. A sample of ammonia (NH3) has a mass of 56.6 g. How many molecules are in this sample? a. 3.32 molecules b. 17.03 x 104 molecules c. 6.78 x 1023 molecules d. 2.00 x 1024 molecules e. 1.78 x 10molecules B. For which compound does 0.256 mole weigh 12.8 g? a. C,H,O b. CO2 c. CH,CI d. C,Ho e. None of these C. One molecule weighs 2.03 x 10 Its molar mass is a. 48.0 g/mole b. 92.1 g/mole c. 114 g/mole d. 122 g/mole e. None of the above D. The limiting reactant in a reaction a. has the lowest coefficient in a balanced equation b. is the reactant for which you have the fewest number of moles c. has the lowest ratio of moles available coefficient in the balanced equation d. has the lowest ratio of coefficient in the balanced equation moles available e. none of these E. Which of the following substances contains the greatest mass percent of oxygen? a. 1 moles H,O b. 2 moles of CS c. 3 moles of NaNO d. 4 moles of NH OH e. 5 moles of NaH F. Balanced chemical equations imply which of the following? a. Numbers of molecules are conserved in chemical change. b. Numbers of atoms are conserved in chemical change. c·Volume is conserved in chemical change d. Exactly two of the above statements are true e. More than two of the above statements are true