Q 4 & 6 p189

Q: Why do all reactions need added energy to get started?

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)

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.

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)

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)

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.

Q 4 & 6 p189

4. Which of the following are exothermic or endothermic?

a. Paper burning

b. Plastic becoming brittle in sun

c. Firecracker exploding

Q 4 & 6 p189

4. Which of the following are exothermic or endothermic?

a. Paper burning

b. Plastic becoming brittle in sun

c. Firecracker exploding

EXO (1 pt)

EXO (1 pt)

ENDO (?)

TOTAL POSSIBLE SCORE = 6 PTS

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