Antoine-Laurant de Lavoisier was an 18 th century French scientist and nobleman who is considered the father of modern chemistry. He recognized and named oxygen and hydrogen, was one of the scientists who developed the metric system and through his experiments confirmed that although matter may change its form, the total mass remains constant. Unfortunately, because he was a nobleman he was beheaded during the French Revolution.

Mass is measured using either a __________ or a __________. In the lab, mass is measured in ______ or __________. grams scale balance kilograms Very Important Information:

Many chemical reactions give off a gas. Because of this, the mass of the remaining solid and liquid products is less than the original mass of the reactants. Before Lavoisier, many scientists thought this was proof that mass was destroyed.

Lavoisier understood what was happening, and correctly hypothesized that the difference in mass was equal to the mass of the gas given. So how did he prove it?

Solving for Mass When all but one of the masses are known, solving for the mass of the unknown takes the most elementary of algebra. 3.4g + ?g = 4.2g2.1g + 8.5g = ?g 3.4g + ?g = 12.0g ? = _____? = _____ ? = _____ ?g = 4.2g – g 10.6 g ?g = 12.0g – 3.4g 8.6 g 2.2g + ?g = 5.6g + 2.7g 1.5g + 6.7g = ?g + 3.3g ? = _____ ?g = 5.6g + 2.7g – 2.2g 6.1 g ?g = 1.5g + 6.7g – 3.3g 4.9 g

1.5 g9.9 g3.0 g8.7 g 3.3 g7.9 g8.9 g9.4 g 7.7 g11.5 g6.6 g

Hydrogen + Oxygen Water 16.0 g 128 g ? g 16.0 grams of hydrogen reacts with 128 grams of oxygen. Assuming all of the reactants are used up, how much water will be produced? Solving for Mass When this concept is shown with a chemical equation, nothing changes about how it should be solved g g = 144 g

2Na + Cl 2 2NaCl If 11.5 grams of sodium are mixed with chlorine gas to make 29.9 grams of sodium chloride, how much chlorine gas was used? Solving for Mass When you are solving for masses, the most important thing to pay a attention to is the placement of the given masses. Sloppiness and laziness will make an easy question turn into a wrong answer. Make sure you place the numbers with the appropriate substance g29.9 g? g 29.9 g – 11.5 g = 18.4 grams

Understanding Coefficients Coefficients multiply through the entire formula of a compound. 2CO 2 =2C and 4 O 3H 2 O =6 H and 3 O 4CaBr 2 =4Ca and 8 Br 5Na 2 O =10 Na and 5 O

Determine how many of each element are in the problems on your notes

Understanding Coefficients Equations without coefficients are known as skeleton equations These equations may or may not represent the correct ratio of moles that interact during the reaction shown. Since mass is directly related to the number of particles, if mass does not change, then the number of particles does not change.

Understanding Coefficients To illustrate the Law of Conservation of Mass, we place coefficients in equations to show that mass is not created or destroyed. These equations are called “balanced equations” because they show the same number of elements on each side.

Understanding Coefficients You can determine whether or not equations are balanced using a simple accounting method and the skill you just learned. Is the following equation balanced? 4 Fe + 3 O 2  2 Fe 2 O 3 ___ Fe ___ ___ O ___ Reactants side Products side Yes, this equation is balanced.

Is the following equation balanced? Al + O 2  Al 2 O 3 ___ Al ___ ___ O ___ Reactants side Products side No, this equation is not balanced. Understanding Coefficients

You can determine whether or not equations are balanced using a simple accounting method and the skill you just learned. Is the following equation balanced? 2 K + 2 H 2 O  2 KOH + H 2 ___ K___ ___ H ___ Reactants side Products side Yes, this equation is balanced. ___ O ___22 4

Is the following equation balanced? Al 4 C 3 (s) + H 2 O (l) → CH 4 (g) + Al(OH) 3 (s) ___ Al ___ ___ C ___ Reactants side Products side No, this equation is not balanced. Understanding Coefficients ___ H ___27 ___ O ___13

_____ Na _____ _____ I _____ YES _____ Ca _____ _____ C _____ _____ O _____ NO _____ C _____ _____ H _____ YES _____ Ag _____ _____ Na _____ _____ I _____ _____ NO 3 _____ NO

When you are given sets of coefficients, all you need to do is plug them in to see if they are balanced or not. Once again, this is a test of your patience more than anything else. ___Li + ___N 2 ___Li 3 N A 6, 2, 2 B 3, 1, 2 C 3, 2, 1 D 6, 1, 2 _____ Li _____ _____ N _____

CH 4 + 2O 2 CO 2 + ____ A 2CO B H 2 O 2 C 2H 2 O D C 6 H 12 O 6 _____ C _____ _____ H _____ _____ O _____ CO H 2 O 2 2H 2 O C 6 H 12 O Always check every answer choice!

CH 4 + 2O 2 CO 2 + ____ _____ C _____ _____ H _____ _____ O _____ A 2CO B H 2 O 2 C 2H 2 O D C 6 H 12 O 6 First, add up everything that is already there Second, figure out what more you need. 4 H’s 2 O’s Third, determine which answer meets this need. 2C + 2O 2H + 2O 4H + 2O 6C + 12H + 6O

6O 2