In other words, atoms are not created nor destroyed in chemical reaction.

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Dustin Hall
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1 CUNTING Physcisal Methods for counting amounts Chemical Methods for counting amounts by numbers 1 pr = 1 doz = 1 1 case = 1 or 4 1 hand = 5 fingers 1 foot = 1 inches Avogadro's number = 6.0x10 +3 anything anything by weighing 1 gummy bear = 1 gram 1 penny = 1 gram 1 proton = 1 amu 1 neutron = 1 amu 1 hydrogen-1 atom = 1 amu 1 carbon-1 atom = 1 amu numbers to amounts by weighing by volume any gas =.4 0 C,1atm carbon-1 = 1 grams carbon-1 exactly (6.0x10 +3 ) (6.0x10 +3 ) the eletrolysis of 36 grams of water will produce molar masses defined by balanced reaction H H + 1 molecule molecules cule multiply through by A number x A number x A number 1 x A number A number equals Avogadro's # x 6.0x10 +3 x 6.0x x 6.0x10 +3 Avogadro's # equals x x 1 x count by weighing x 18 grams x grams 1 x 3 grams H H per per per H H 4 grams of hydrogen and 3 grams oxygen Chemical Methods for counting amounts by balanced reaction H H + 1 This is a chemical recipe for the decomposition of water by electrolysis. molecule molecules cule multiply through by A number x A number x A products number 1 x A number A number equals Avogadro's # x 6.0x10 +3 x 6.0x x 6.0x10 +3 Avogadro's # equals x x 1 x reactants What did John Dalton in 1808 have to say about chemical reactions? 1.. Is this Chemical Atoms true are for reactions conserved the decomposition involve a chemical just of the water reaction. simple by rearrangement electrolysis? of atoms. In other words, atoms are not created nor destroyed in chemical reaction. count by weighing x 18 grams x grams 1 x 3 grams H H per H per per + 1 H H 1

2 1. Chemical reactions involve just the simple rearrangement of atoms.. Atoms are conserved in a chemical reaction. In other words, Let s atoms see are if John not created Dalton had nor destroyed assumed correctly. in chemical reaction. This ture for the above decomposition of water by electrolysis. H H + 1 H H H H H H H H 4 hydrogen atoms 4 hydrogen atoms oxygen atoms oxygen atoms The chemical equation is the shorthand notation for a chemical reaction. Reactants react to produce Products Law of Conservation of Mass - Matter cannot be gained or lost in the process of a chemical reaction. The law of conservation of mass states that we must have a balanced equation. List five factors involved in the construction of an equation or "chemical recipe." 1. The identity of products and reactants must be specified.. 3. Reactants are written to the left of the reaction arrow (---->) and products to the rig The physical state of reactants and products is shown is parentheses; (s), (l), (g), (a 4. The symbol over the reaction arrow means that heat energy is necessary for the reaction to occur. 5. The equation must be balanced.

3 Steps for balancing a chemical equation Step 1: Count the number of atoms of each element on both the product and reactant sid Step : Determine which atoms are not balanced. Step 3: Balance one atom at a time, using coefficients. Start with atoms that appear only once in the reactants and only once in the products. Usually leave Hydrogen atoms followed by xygen atoms until last. Step 4: After you believe that you have successfully balanced the equation, repeat Step 1, to be certain that mass conservation has been achieved. Note: D NT Change subscripts in a molecular formula (i.e., NaCl X Na Cl ) Don t do this!!!! Mg + 1 Mg In balancing, we would like the lowest whole number molar ratio. Where the number out in front is called a molar coefficient. Mg + 1 Mg 3

4 But what if an individual balanced the magnesium first? 1 1 Mg Mg The reaction is balanced, BUT there is a fractional molar coefficient. We must remove the fraction by multiplying through by Mg + 1 Mg 1 I feel this way is the easiest way to balance, if you: 1) always balance oxygens last; ) then multiply by factor of, to remove any fractional molar coefficient that might be present in the balanced reaction. Fe Fe Fe Fe 3 Note: We are going for the lowest whole number Molar coefficient ratio 4

5 Finally, name the compounds and give physical states. Mg + 1 Mg (s) magnesium metal solid oxygen gas Fe + 3 (s) (g) 4 3 (g) iron metal solid oxygen gas (s) magnesium oxide solid ionic salt 1 Fe 3 (s) iron (III) oxide solid TM ionic salt Combustion of methane gas 1CH 4 +? 1 1 Always balance oxygens last 1C + H 1 + 1? = 4 + = 4 5

6 Combustion of ethane gas 1C H 6 +? 7 Always balance oxygens last? 7 = 7 C + 3H = 7 1C 7 H 6 + C + 3H Combustion of methanol liquid 1CH 4 +? 33 1C + H 1 1 Always balance oxygens last ? = 4 + = 4 1 +? = 4 Now solve for? -1-1 Substract one from each side? = 3 Divide each side by? = 3 6

7 Combustion of methanol liquid 1CH 4 +? 33 1C + H 1 1 x 1 x 3 x 1 x 1CH 4 + 1C + H 3 4 Now balance the combustion of glucose (blood sugar) 1C 6 H 1 6 +? Always balance oxygens last 1 6 +? = 18 6C + 6H = ? = 18 Now solve for? -6-6 Substract 6 from each side? = 1 Divide each side by? = 6 7

8 Ionic salt transfer reactions in aqueous solution A + B - (aq) + C + D - (aq) AD(?) + BC(?) Ionic salt solubility in water All group I salts soluble, Li,Na,K All nitrate salts soluble All ammonium salts soluble,nh 4 + Driving forces for ion transfer, a force that makes the reaction go. Physical state formations: If a solid forms If a liquid forms If a gas forms you ll need to determine state based on some rules Evidence for chemical change, Color change (tricky) Heat evolved (tricky) precipitation saturation (solids) If a liquid forms (heat evolved) If a gas forms (bubbles, odor) Ionic salt transfer reactions in aqueous solution A + B - (aq) + C + D - (aq) AD(?) + BC(?) Use of common sense tells us that, we will mix ionic solutions in order to have reaction occur. (we are not going to mix for the sake of mixing) Use of common sense tells us that, An acids mixed with a base (antacid) causes a neutralization. H + A - (aq) + M + H - (aq) H (l) + MA(?) Use of common sense tells us that, An acids mixed with carbonate (HC 3- ) produces C water and salt H + A - (aq) + NaHC 3 (aq) H (l) + NaA(aq) C (g) 8

Chapter 3. Mass Relationships in Chemical Reactions

Chapter 3. Mass Relationships in Chemical Reactions Chapter 3 Mass Relationships in Chemical Reactions In this chapter, Chemical structure and formulas in studying the mass relationships of atoms and molecules. To explain the composition of compounds and