CONSERVATION OF MASS

PHYSICAL VS. CHEMICAL REACTIONS

PHYSICAL

• CONCERNED WITH ENERGY AND STATES OF MATTER. DOES NOT PRODUCE A NEW SUBSTANCE.

• CHANGING STATES: MELTING, FREEZING, VAPORIZING, CONDENSATING, SUBLIMATING

• EXAMPLES: CRUSHING A CAN, MELTING AN ICE CUBE, BREAKING A BOTTLE

CHEMICAL

• INVOLVES THE REORGANIZATION OF THE ATOMS TO CREATE A NEW SUBSTANCE.

• C + O2 CO2

• EXAMPLES: RUSTING OF METAL, BURNING OF PAPER, COMBUSTION OF FUEL, METABOLISM OF FOOD

REACTANTS AND PRODUCTS

• REACTANTS COMBINE TO FORM A PRODUCT

• 2H + O H20

• REACTANTS PRODUCT

• COEFFICIENT = THE BIG NUMBER IN FRONT OF THE ELEMENT SYMBOL (2H)

• SUBSCRIPT = THE LITTLE NUMBER AFTER THE ELEMENT SYMBOL (H2)

• BOTH NUMBERS TELL YOU HOW TO COUNT ATOMS

• NUMBER OF ATOMS ON REACTANTS SIDE = NUMBER OF ATOMS ON PRODUCT SIDE

COKE AND MENTOS

• THE NUMEROUS SMALL PORES ON THE CANDY'S SURFACE

CATALYZE THE RELEASE OF CARBON DIOXIDE (CO2) GAS FROM

THE SODA, RESULTING IN THE RAPID EXPULSION OF COPIOUS QUANTITIES OF FOAM. ALTHOUGH ANY CARBONATED BEVERAGE WILL PRODUCE A SIMILAR EFFECT, THE REACTION WAS POPULARIZED USING DIET COKE FOR SEEMINGLY PRODUCING THE BEST RESULTS.

A PHYSICAL REACTION

ELEPHANT TOOTHPASTE

• THE OVERALL EQUATION FOR THIS REACTION IS:

• THE DECOMPOSITION OF THE HYDROGEN PEROXIDE INTO WATER AND OXYGEN IS CATALZYED BY THE IODIDE ION.

• THE DISHWASHING DETERGENT CAPTURES THE OXYGEN AS BUBBLES.

A CHEMICAL REACTION

LAW OF CONSERVATION OF MASS

• MATTER CANNOT BE CREATED OR DESTROYED DURING A CHEMICAL REACTION.

• MATTER MAY CHANGE FORM.

• THE MASS OF THE SUBSTANCES IS THE SAME BEFORE AND AFTER A CHEMICAL REACTION.

REACTANTS AND PRODUCTS

• REACTANTS COMBINE TO FORM A PRODUCT

• REACTANTS PRODUCT

• NUMBER OF ATOMS ON REACTANTS SIDE = NUMBER OF ATOMS ON PRODUCT SIDE

COUNTING ATOMS

LOOK AT THE SUBSCRIPT NUMBERS. THIS TELLS YOU HOW MANY ATOMS THERE ARE OF EACH ELEMENT. IF THERE IS NO SUBSCRIPT NUMBER, THEN THERE IS ONLY ONE ATOM OF THAT ELEMENT.

• FE2S3 = 2 IRON ATOMS AND 3 SULFUR ATOMS

PRACTICE

• NH4SO4

WRITE DOWN WHICH ATOMS ARE IN THE COMPOUND AND HOW MANY THERE ARE OF EACH.

PRACTICE

• CAFFEINE – C8H10N4O2

WRITE DOWN WHICH ATOMS ARE IN THE COMPOUND AND HOW MANY THERE ARE OF EACH.

COMPOUNDS WITH MORE THAN TWO ELEMENTS ALMOST ALWAYS HAVE POLYATOMIC IONS.

CA(OH)2

POLYATOMIC ION (HYDROXIDE)

• THIS IS IMPORTANT WHEN COUNTING ATOMS.

CA(OH)2 = 1 CALCIUM, 2 OXYGEN,

2 HYDROGEN ATOMS

• THE SUBSCRIPT NUMBER ONLY APPLIES TO THE ELEMENTS IN PARENTHESES.

• MG(OH)2

WRITE DOWN WHICH ATOMS ARE IN THE COMPOUND AND HOW MANY THERE ARE OF EACH.

• AL2(SO4)3

WRITE DOWN WHICH ATOMS ARE IN THE COMPOUND AND HOW MANY THERE ARE OF EACH.

• (NH4)3PO4

WRITE DOWN WHICH ATOMS ARE IN THE COMPOUND AND HOW MANY THERE ARE OF EACH.

BALANCING CHEMICAL EQUATIONS• A BALANCED EQUATION HAS THE SAME NUMBER OF ATOMS OF EACH

ELEMENT ON THE REACTANT AND THE PRODUCT SIDE

• COEFFICIENTS (BIG NUMBERS IN FRONT OF A FORMULA) ARE USED TO BALANCE AN EQUATION

• THE COEFFICIENT APPLIES TO EVERY ELEMENT IN A COMPOUND

• 2H2 (G) + O2 (G) 2H20 (G)

• DO NOT CHANGE SUBSCRIPTS TO BALANCE AN EQUATION

JEFFERSON LABS PRACTICE

•GO TO jlab.org

•Click on Student Zone

•Click on Element Balancing Game

•Choose 15 Beginner equations

•Click on Let’s Start!

PHAROAH’S SNAKE

• HTTP://WWW.YOUTUBE.COM/WATCH?V=RITALJHHK7S

PHAROAH’S SNAKE(MERCURY THIOCYNATE)

•PHARAOH'S SNAKE CHEMICAL REACTION

• IGNITING MERCURY(II) THIOCYANATE CAUSES IT TO DECOMPOSE INTO AN INSOLUBLE BROWN MASS THAT IS PRIMARILY CARBON NITRIDE,

C3N4.

•MERCURY(II) SULFIDE AND CARBON DISULFIDE ARE ALSO PRODUCED.

• 2HG(SCN)2 → 2HGS + CS2 + C3N4