"a, b, c, and d" represent the coefficients used to balance the equation. The brackets "" represent the concentration of the species (moles per liter or molarity). The general equilibrium expression for a reaction: Then we convert to grams to find the amount of oxygen that needs to be added: Then, because there are five (5) molecules of oxygen to every two (2) molecules of C 2H 2, we need to multiply the result by 5/2 to get the total molecules of oxygen. Therefore we know that 1 mole of C 2H 2 weighs 26 g (2 × 12 grams + 2 × 1 gram). To be able to calculate the moles we need to look at a periodic table and see that 1 mole of C weighs 12.0 g and H weighs 1.0 g. To solve this problem, it is necessary to determine how much oxygen should be added if all of the reactants were used up (this is the way to produce the maximum amount of CO 2).įirst, we calculate the number of moles of C 2H 2 in 6.0 g of C 2H 2. If she uses the equation below, how much oxygen should she add to the reaction?ĢC 2H 2(g) + 5O 2(g) -> 4CO 2(g) + 2 H 2O(l) Often, it is necessary to identify the limiting reagent in a problem.Įxample: A chemist only has 6.0 grams of C 2H 2 and an unlimited supply of oxygen and he desires to produce as much CO 2 as possible. Sometimes when reactions occur between two or more substances, one reactant runs out before the other. How many moles of Ca are in 4.50 grams of Ca?Ĭitation: Department of Chemistry at UNC Chapel Hill at Molar Mass of Ca = 40.08 (From the Periodic Table) So, 40 grams of calcium makes one mole, 80 grams makes two moles, etc. For example, calcium has an atomic mass of 40 atomic mass units. Given the atomic or molecular mass of a substance, that mass in grams makes a mole of the substance. This conversion can be easily done when the atomic and/or molecular mass of the substance(s) are known. Thus, you have the same number of moles of AgNO 3, NaCl, AgCl, NaNO 3.Ĭonverting between moles and grams of a substance is often important. In the equation above there are no numbers in front of the terms, so each coefficient is assumed to be one (1). Similarly, if you have a mole of carrots, you have 6.022 x 10 23 carrots. If you have a dozen carrots, you have twelve of them. A mole is similar to a term like a dozen. Given enough information, one can use stoichiometry to calculate masses, moles, and percents within a chemical equation.Ī mole simply represents Avogadro's number (6.022 x 10 23) of molecules. View Notes.Stoichiometry is simply the math behind chemistry. Technical information, teaching suggestions, and related resources that complement this Concept Builder are provided on the Notes page. Learners and Instructors may also be interested in viewing the accompanying Notes page. However, the 18 different groups of questions can be printed. There is no need for an activity sheet for this Concept Builder. Users are encouraged to open the Concept Builder and explore. The built-in score-keeping makes this Concept Builder a perfect candidate for a classroom activity. Question-specific help is provided for each of the 18 situations. There are a total of 36 questions organized into 18 different Question Groups and spread across the three difficulty levels. Each difficulty level builds on the previous level. The Balancing Chemical Equations Concept Builder provides learners with experience balancing chemical equations by entering coefficients and conducting an atom count for each element on the reactant and the product side of the equation. Concept Builders » Chemistry » Balancing Chemical Equations
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