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Q 4 & 6 p189 Q: Why do all reactions need added energy to get started?

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Presentation on theme: "Q 4 & 6 p189 Q: Why do all reactions need added energy to get started?"— Presentation transcript:

1 Q 4 & 6 p189 Q: Why do all reactions need added energy to get started?

2 Q 4 & 6 p189 Q: Why do all reactions need energy to get started?
A: Because at least one chemical bond has to be broken before the reaction can proceed (1 pt)

3 Q 4 & 6 p189 6. Calcium oxide, CaO, is used in cement mixes. When water is added, heat is released as CaO forms calcium hydroxide, Ca(OH)2. What signs are there that this is a chemical reaction? Which has more chemical energy, the reactants or products? Explain your answer.

4 Q 4 & 6 p189 6. Calcium oxide, CaO, is used in cement mixes. When water is added, heat is released as CaO forms calcium hydroxide, Ca(OH)2. What signs are there that this is a chemical reaction? Which has more chemical energy, the reactants or products? Explain your answer. ANSWERS: Signs: Heat and new substance. (1 pt) Energy: Reactants have more chemical energy since some chemical energy is converted and released as heat during reaction. (1 pt)

5 Q 4 & 6 p189 6. Calcium oxide, CaO, is used in cement mixes. When water is added, heat is released as CaO forms calcium hydroxide, Ca(OH)2. What signs are there that this is a chemical reaction? Which has more chemical energy, the reactants or products? Explain your answer. BTW: CaO has also been used in self-heating hot beverage cans. But, they sometimes blew up or melted, and are no longer on the market. ANSWERS: Signs: Heat and new substance. (1 pt) Energy: Reactants have more chemical energy since some chemical energy is converted and released as heat during reaction. (1 pt)

6 Q 4 & 6 p189 Which of the following are exothermic or endothermic?
Paper burning Plastic becoming brittle in sun Firecracker exploding

7 TOTAL POSSIBLE SCORE = 6 PTS
Q 4 & 6 p189 Which of the following are exothermic or endothermic? Paper burning Plastic becoming brittle in sun Firecracker exploding EXO (1 pt) ENDO (?) EXO (1 pt) TOTAL POSSIBLE SCORE = 6 PTS

8 310: 20 g CaO CaO + H2O > Ca(OH)2 • 1 mole CaO = (40 + 16) g = 56 g
• 20 g CaO = 20 / 56 = 0.36 mole • 1 mole H2O = 18 g • 0.36 mole H2O = 0.36 • 18 = 6.5 g = 6.5 ml


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