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Chemistry Math Manual

Chemistry Math Manual. A robot’s guide to solving chemistry math problems . . . . . . and other “cookbook” procedures. Init 12/12/2012 by Daniel R. Barnes.

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Chemistry Math Manual

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  1. Chemistry Math Manual A robot’s guide to solving chemistry math problems . . . . . . and other “cookbook” procedures Init 12/12/2012 by Daniel R. Barnes NOTE: I would rather you develop general-purpose problem-solving skills so that you can solve ANY problem put before you, not just the limited number of problem types addressed in this “recipe” book. However, this collection of instructions might have to do in the meantime.

  2. Equation-Balancing Steps 1. Copy the equation, leaving lots of room in front of each formula for your coefficients. 2. List the elements in the equation, in the same order, under the left side and under the right side of the equation. 3. Count the number of atoms of each element on each side of the equation. 4. Is the equation balanced? Yes  END. No  proceed. 5. Change a coefficient. Try to make one of the elements balanced by increasing the coefficient in front of a formula that has an element that there’s not enough of. 6. Update the atoms counts of the elements that were affected by the coefficient change. Go to step 4.

  3. Equation-Balancing Tips * Try to balance first those elements that occur in the fewest number of formulas. * Try to balance last those elements that occur in the greatest number of formulas. They might even get balanced by accident as you balance the other elements first. * If a polyatomic ion is present in both the reactants and the products, you might be able to regard it as a unit when balancing the reaction, making your job simpler and quicker. * ADVANCED ONLY: For insanely difficult equations, you might need to represent each coefficient with a Greek letter and develop an equation for each element, incorporating those Greek letters, showing how the number of atoms of that element on the left equal the number of atoms of that element on the right. Solve for the ratio of the Greek letters by substitution and the other algebraic tricks you use for multi-variable, multiple-equation systems.

  4. Molar Mass 1. Copy the formula. 2. Break the formula down into its elements. 3. Count the number of atoms of each element. 4. Multiply each atom count by the average atomic mass of the element in question. 5. Add the results and express the answer in grams per mole.

  5. COMING SOON: *Stoichiometry *Concentration calculation (E-mail me at barnesd@centinela.k12.ca.us if you need me to expedite the creation of these instruction lists.)

  6. Gas Math • Translate English into math. (Declare your variables.) • (NOTE: At this stage, immediately convert all Celsius temperatures to Kelvin by adding 273!) • Write the correct formula from the reference sheet. • (At this point, you might realize you’re really doing heat math.) • If you’re using the combined gas law, cross out anything that remains constant (or anything that is not even mentioned). 4. Rearrange the formula to isolate the unknown. 5. Plug in the numbers. (Include the units!) 6. Cancel units and zeros; combine uncanceled units. 7. Do the arithmetic. 8. Box the answer.

  7. Heat Math 1. Translate English into math. (Declare your variables.) 2. Choose the correct formula. (At this point, you might realize that you’re actually doing gas math.) 3. Rearrange the formula to isolate the unknown. • Plug in the numbers, along with their units. • (NOTE: at no point should you make units appear or disappear for no legitimate reason.) • Cancel units and zeros as possible. • Combine uncanceled units. 6. Do the arithmetic. Show all your work. Otherwise, it will look like you illegally used a calculator. 7. State your answer as a complete sentence and box it.

  8. LeChâtelier Problems • Determine if it’s a LeChatelier problem or not. • Signs that it is: (a) the word “equilibrium”, (b) double arrows (showing a reversible reaction), (c) a change in • (i) pressure, (ii) temperature, or (iii) concentration. • Whatever change was inflicted on the system, the chemicals in the system will try to do the exact opposite. • (NOTE: Pressure disturbances are responded to by changes in number of gas molecules.) 3. Figure out which way the equilibrium needs to shift (to the left or to the right?) in order to do the opposite of what was done to the chemicals. • Determine secondary consequences. • (Changes in (a) concentrations of of chemicals, • (b) pressure, and (c) temperature • that were not part of the original disturbance.)

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