1. Chapter 24: Chemical Reactions

2. Chemical Reactions
evidence of chemical reactions

3. Section 1: Chemical Changes
Chemical reaction: a change in which one or more substances are converted into new substances
The substances that react together are called reactants
The new substances produced are called products
The mass of the reactants before the reaction MUST equal the products, according to the law of conservation of mass

4. Chemical Reactions glycerol and potassium permanganate
dehydration of sugar
sodium acetate

5. Describing Chemical Reactions
French chemist Antoine Lavoisier discovered this law in the late 1700s.
He heated 10 grams of mercury (II) oxide in a sealed container
The compound bubbled and changed from a red powder (HgO) to a silver liquid (Hg)
He had 9.3 grams of mercury, and 0.7 grams of oxygen ( = 10.0 g)
Therefore, matter is conserved in a chemical reaction
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6. Chemical Reactions pharaoh's snake Chemiluminescence
phosphorus in oxygen

7. Writing Equations
Just like we write chemical formulas to save space, we can write chemical equations to show a chemical reaction
2HgO (s)  2Hg (l) + O2 (g)
2 units of solid mercury (II) oxide produce 2 units of liquid mercury and 1 unit of oxygen gas
The 2’s in front of the HgO and the Hg are called coefficients
The letters in ( ) tell us the state of matter
(aq) means “dissolved in water”

8. Chemical Reactions
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9. Cd(NO3)2(aq) + H2S(g)  CdS(s) + 2HNO3(aq)
Review Questions
Answer these questions for tomorrow:
Cd(NO3)2(aq) + H2S(g)  CdS(s) + 2HNO3(aq)
Identify these items:
Reactants
Products
Names
States of matter
If you started with 15 grams of reactants, how much product should you get?
What might happen if chemical reactions did not obey the law of conservation of mass?