* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Partial Pressures of Gases
Hydrogen-bond catalysis wikipedia , lookup
Physical organic chemistry wikipedia , lookup
Chemical bond wikipedia , lookup
Spinodal decomposition wikipedia , lookup
Rutherford backscattering spectrometry wikipedia , lookup
Process chemistry wikipedia , lookup
Chemical thermodynamics wikipedia , lookup
Chemical reaction wikipedia , lookup
Chemical equilibrium wikipedia , lookup
Lewis acid catalysis wikipedia , lookup
Electrolysis of water wikipedia , lookup
Debye–Hückel equation wikipedia , lookup
Double layer forces wikipedia , lookup
Bioorthogonal chemistry wikipedia , lookup
Click chemistry wikipedia , lookup
Relativistic quantum mechanics wikipedia , lookup
Electrochemistry wikipedia , lookup
Transition state theory wikipedia , lookup
Evolution of metal ions in biological systems wikipedia , lookup
Rate equation wikipedia , lookup
IUPAC nomenclature of inorganic chemistry 2005 wikipedia , lookup
History of molecular theory wikipedia , lookup
Strychnine total synthesis wikipedia , lookup
Metalloprotein wikipedia , lookup
SNC2D 1.7 Balancing Chemical Equations Writing a balanced equation is almost always a useful skill for anyone working with chemicals. Let’s use the method of balancing equations “by inspection,” which means that we will simply count the number of atoms of each element before and after the reaction and adjust coefficients to make sure the numbers are the same for each element. Let’s examine an equation for the reaction between copper metal and silver nitrate solution. First, we observe metallic copper wire, Cu(s), being immersed in a colourless solution of silver nitrate, AgNO3(aq). The solution gradually changes colour to blue, and sparkling crystals form on the copper wire. Diagnostic tests confirm that the blue solution is due to formation of copper(II) nitrate, Cu(NO3)2(aq), which goes into solution, and the crystals are metallic silver, Ag(s). This reaction is used industrially to recover and recycle silver by trickling waste solutions containing silver ions over scrap copper. Step 1 Write a reaction equation, including states of matter: ? Cu(s) + ? AgNO3(aq) → ? Ag(s) + ? Cu(NO3)2(aq) Step 2 First, balance atoms that are not in polyatomic ions, and are not O or H. (Oxygen and hydrogen atoms may be constituents of many compounds in a reaction. Balancing O and H early could be a waste of time, because they might need to be rebalanced again at a later stage.) In this case, we can start with Cu and Ag, but as stated they are already balanced (one atom of each on each side of the equation). Our equation remains unchanged. ? Cu(s) + ? AgNO3(aq) → ? Ag(s) + ? Cu(NO3)2(aq) Step 3 Next, balance any polyatomic ions. In this case, there are two (NO3)– ions in the product, but only one in the reactant, so the quantity of the reactant compound needs to be doubled: ? Cu(s)+ 2 AgNO3(aq) → ? Ag(s) + ? Cu(NO3)2(aq) Doubling AgNO3 requires doubling of the Ag after reaction: ? Cu(s) + 2 AgNO3(aq) → 2 Ag(s) + ? Cu(NO3)2(aq) Step 4 Next, balance O atoms and H atoms. We have none in this case. Then balance any remaining elements, such as H2 or O2. Again, we have none, so we can state our final equation: Cu(s) + 2 AgNO3(aq) → 2 Ag(s) + Cu(NO3)2(aq) SNC2D Step 5 Final check: Reactants: 1 Cu, 2 Ag, 2 (NO3) Products: 1 Cu, 2 Ag, 2 (NO3) The equation is balanced as stated. This approach generally reduces the time spent in a random trial and error method. There is one more tip on balancing some reaction equations that appear to require fractional coefficients. For example, the following balanced equation requires 7 atoms of oxygen contained in 7 molecules of O2. 2 2 NH3(g) + 7 2 O2(g) → 3 H2O + 2 NO2(g) To avoid fractional coefficients, we double all coefficients, thereby obtaining a balanced equation of whole number coefficients while retaining the same mole ratio for the reaction. 4 NH3(g) + 7 O2(g) → 6 H2O + 4 NO2(g) Steps for Balancing Chemical Equations by Inspection 1. Write the chemical formula for each reactant and product, including the state of matter for each one. 2. Try balancing any atom that is not in a polyatomic ion and is not carbon, oxygen or hydrogen.(ECHO) 3. If possible, balance polyatomic ions as a group. 4. Balance the remaining atoms and molecules, taking into account the oxygen and hydrogen atoms and water; leave any elements in the equation, such as H 2 or O2 until the end. 5. Check the final reaction equation to ensure that there is the same number of each type of atom before and after the reaction. Sample Problem 1 Write a balanced equation for the reaction of aqueous sodium phosphate and aqueous calcium chloride to produce sodium chloride in solution and a precipitate of calcium phosphate. ? Na3PO4(aq) + ? CaCl2(aq) → ? Ca3(PO4)2(s) + ? NaCl(aq) Solution : Using the steps outlined above you should be able to balance the equation to get 2 Na3PO4(aq) + 3 CaCl2(aq) → Ca3(PO4)2(s) + 6 NaCl(aq) SNC2D Worksheet 1.7: Balancing Chemical Equations Balance the following equations by inspection. 1. __Ni(s) + __HCl(aq) 2(aq) + __H2(g) 2. __Ca(OH)2(s) + __HCl(aq) 2(aq) 3. __Cl2(g) + __NaBr(aq) 4. __Cr2O3(s) | (s) 2(l) + __NaCl(aq) + __O2(g) 5. __Fe(s) + __HCl(aq) 3(aq) 6. __C3H6(g) + __O2(g) 7. __P4(s) + __F2(g) + __HOH(l) 2(g) + __H2(g) + __H2O(g) 3(l) 8. __Ca(NO3)2(aq) + __KOH(aq) 9. __KHCO3(s) 2(s) + __KNO3(aq) K2CO3(s) + __H2O(l) + __CO2(g) 10. __H3PO4(aq) + __NaOH(aq) 3PO4(aq) 11. __Ca(NO3)2(aq) + __Na3PO4(aq) 12. __Cu(s) + __HNO3(aq) + __HOH(l) 3(PO4)2(s) 3)2(aq) + __NaNO3(aq) + __NO2(g) + __H2O(l) [this one is tricky!]