Imagine Magazine - Johns Hopkins - March/April 2014 - (Page 47)

knossos games Stoichiometry by Tim Boester Stoichiometry is the branch of chemistry that deals with balancing chemical equations. In a chemical reaction, the atoms that make up the chemical reactants may move around and recombine in different ways. In other words, no atoms are created or destroyed. For example, nitrogen gas (N2) can be combined with hydrogen gas (H2) to form ammonia gas (NH3). This is represented by the chemical equation N2 + H2 © NH3 However, this chemical equation is unbalanced: two atoms of nitrogen and two atoms of hydrogen go into the chemical reaction, but the ammonia contains only one atom of nitrogen and three atoms of hydrogen. In order to balance the chemical equation, we need the same number of atoms of each element on both sides: 1 N2 + 3 H2 © 2 NH3 Now this chemical equation is balanced; each side has two atoms of nitrogen and six atoms of hydrogen. This balanced equation shows us that what really happens in this reaction is that one molecule of nitrogen gas combines with three molecules of hydrogen gas to produce two molecules of ammonia gas. In the following puzzle, each chemical equation needs to be balanced. The number of molecules of each chemical, in the order presented in the chemical equation, should be put into the grid, going either across or down (like in a crossword puzzle). Even if the number of molecules is a two-digit number, that value goes in a single box in the grid. Notice that some values in the grid will represent the number of molecules of one chemical going across, and the same number of molecules of a different chemical going down. In order to keep all of the chemical equations balanced in the grid, you may have to use multiples of a balanced equation. For example, the above chemical equation could also be balanced with the values 2 N2 + 6 H2 © 4 NH3, or 3 N2 + 9 H2 © 6 NH3. a h Across b. __ O2 + __ NH3 © __ NO + __ H2O f. __ KClO3 © __ KCl + __O2 g. __H2S + __ NaOH © __ H2O + __ Na2S h. __ NaCl + __ H2SO4 © __ Na2SO4 + __ HCl j. __ CaCO3 © __ CaO + __CO2 k. __ Na + __ Na2SiF6 © __ Si + __ NaF Down a. __ FeCr2O4 + __ K2CO3 + __ O2 © __ K2CrO4 + __ Fe2O3 a + __ CO2 b c d e c. __ Pb(NO3)2 + __ H3AsO4 © __ PbHAsO4 + __ HNO3 d. __ Cl + __ O2 © __ ClO2 f e. __ Al + __ NH4ClO4 © __ Al2O3 + __ AlCl3 + __ NO + __ H2O g. __ Ca + __ H2g © __ Ca(OH)2 + __ H2 O i. __ H2 + __ CO © __CH3OH j Ryan revision 2 Paul revision 3 Steven revision 4 Quincy revision 5 apartment $18 chalet $14 chalet $14 yacht $18 yacht $13 yacht $12 Paul estate $15 estate $15 villa $15 villa $15 villa $15 estate $19 Quincy villa $16 villa $16 estate $19 estate $17 chalet $17 chalet $16 Ryan Steven yacht $17 yacht $13 yacht $13 chalet $13 estate $18 villa $17 Thomas chalet $13 www.cty.jhu.edu/imagine i k Thomas revision 1 apartment apartment apartment apartment apartment $18 $21 $16 $16 $15 e j original Ryan d g Solution to Knossos Games 21.3 Quincy c f h Paul b k 4 5 4 4 6 8 4 4 6 7 2 4 4 2 8 4 4 8 2 2 2 2 6 8 2 2 12 12 i Tim Boester is an Assistant Professor in Mathematics Education at Wright State University. Steven Thomas imagine 47 http://www.cty.jhu.edu/imagine

Table of Contents for the Digital Edition of Imagine Magazine - Johns Hopkins - March/April 2014

In My Own Words
Chemistry Is…
Master of Reactions
Fascinated by Photochemistry
What About Labs?
Buckyballs and Nanocrystals
Small Is Big
Chemistry Among the Stars
Making Chemicals Safer, 21st Century Style
Selected Opportunities & Resources
Empowered to Change the World
The Buzz About History
Off the Shelf
Word Wise
Exploring Career Options
One Step Ahead
Planning Ahead for College
Students Review
Mark Your Calendar
Knossos Games

Imagine Magazine - Johns Hopkins - March/April 2014