CHEM 1001 Chapter : CHEM 1001 Chapter 5 Notes

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15 Mar 2019

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Chemical sentences- equations: chemical equations represent the sentences in the language of chemistry. Never change the subscripts: no2 (the 2 is the subscript) Avogadro"s number: avogadro"s number is defined as the number of atoms in a 12-g sample of carbon-12 and is 6. 02x10^23. The mole: a mole (mol) is defined as the amount of a substance that contains 6. 02x10^23 particles, 1 mol= 6. 02x10^23 atoms/particles/molecules, 6. 02x10^23 baseballs is roughly equal to the mass of our earth. Percent composition: percentage= part/whole x100, percentage of each element in a compound, by mass, can be determined from, 1. Mass percent as a conversion factor: the mass percent tells you the mass of a constituent element in. The mole: molar volume of a gas: one mole of any gas occupies a volume of. 22. 4l at standard temperature and pressure (stp: stp is defined as 1 atmosphere (atm) of pressure and a temperature of 0 degrees celsius or 273 degrees kelvin.

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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 â 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 + O2â 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 â 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, â PbO + 02 C. Ca + H2O â 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

What is the balanced chemical equation for the reaction used to calculate ÎHâf of CaCO3(s)? If fractional coefficients are required, enter them as a fraction (i.e. 1/3). Indicate the physical states using the abbreviation (s), (l), or (g) for solid, liquid, or gas, respectively without indicating allotropes. Use (aq) for aqueous solution. Express your answer as a chemical equation. The standard enthalpy of formation (ÎHâf) is the enthalpy change that occurs when exactly 1 mol of a compound is formed from its constituent elements under standard conditions. The standard conditions are 1 atm pressure, a temperature of 25 âC , and all the species present at a concentration of 1 M . A "standard enthalpies of formation table" containing ÎHâf values might look something like this: Substance ÎHâf H(g) 218 kJ/mol H2(g) 0 kJ/mol Ca(s) 0 kJ/mol Ca2+(aq) â543 kJ/mol C(g) 71 kJ/mol C(s) 0 kJ/mol N(g) 473 kJ/mol O2(g) 0 kJ/mol O(g) 249 kJ/mol S2(g) 129 kJ/mol

CHEM 1001 Chapter : CHEM 1001 Chapter 5 Notes

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