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Tema [17]
3 years ago
6

Name the phase transition in each of the following situa- tions and indicate whether it is exothermic or endothermic: (a) Bromin

e vapor turns to bromine liquid as it is cooled. (b) Crystals of iodine disappear from an evaporat- ing dish as they stand in a fume hood. (c) Rubbing alcohol in an open container slowly disappears. (d) Molten lava from a volcano turns into solid rock.
Chemistry
1 answer:
bezimeni [28]3 years ago
5 0

Answer:

(a)  Condensation:Exothermic

(b)  Sublimation: Endothermic

(c)  Vaporization: Endothermic

(d) Freezing: Exothermic

Explanation:

When a phase change occurs, for example going from a liquid to a gas we need to increase the kinetic energy of the molecules to escape to the gas phase where the kinetic energy of the molecules is greater. By the contrary if we remove energy we slow down the molecules increasing their atttraction and slowing them as it occurs when the  goes into the liquid state, hence this phase change is exothermic.

(a)  Condensation : when the phase change is from a gas by definition we have a condensation phase chanhe. The reaction is exothermic, we need to cool the gas to condense.

(b)  Sublimation: crystals of iodine disappear from an evaporating dish as they stand in a fume hood : this phase change receives the name of sublimation and it occurs when a solid goes directly to the gas phase without going through the liquid phase. We need to increase the energy of the molecules so it can go to the gas phase and the change is endothermic.

(c)  Vaporization : rubbing alcohol in an open container slowly disappears: this phase change is vaporization and by difinition is when the liquid goes to the gas phase, hence its name vaporization. The change is endothermic, we need heat  from the sorroundings to give the molecules of the liquid enough energy to escape into the vapor phase.

(d) Molten lava from a volcano turns into solid rock : this phase change is freezing and we need to lower the energy of the liquid by releasing it to the sorroundings, therore it is an exothermic phase change.

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Use the specific heat capacity that you calculated for granite to determine how many grams of granite at the initial temperature
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Answer:

Explanation:

specific heat of granite s = .79 J / g / k

let the mass of granite = m

heat lost by granite = heat gained by water

heat lost = mass x specific heat x drop in temperature

= m x .79 x (80 - 20.45)

heat gained by water

= 3000 x 4.186 x (20.45- 20)

heat lost by granite = heat gained by water

m x .79 x 59.55  =  3000 x 4.186 x .45

m = 120.12 g .

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3 years ago
You have at your disposal 3 1-pound bags of various pure salts that dissolve readily in water. You can add one of the bags to a
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Answer:

This question appears incomplete

Explanation:

However, it should be noted that addition of soluble salts generally lowers the freezing point of water hence after the addition, water will no longer freeze at 0°C but lower.

Soluble salts tend to form more ions in water, it is these ions that are responsible for interfering with the hydrogen bonds hence lowering the freezing. Thus, (since each bag are of the same weight) <u>the bag that contains the salt that ionizes more in water will lower the freezing point by the greatest amount</u>.

NOTE: Different weight of the salts could lead to more ions been formed in the water by some salts as against the other.

6 0
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V CH4(g) = 190.6 L

Explanation:

assuming ideal gas:

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∴ moles (n) = 7.80 mol CH4(g)

∴ Volume CH4(g) = ?

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Answer:

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= 2.65 × 24

= 63.6 dm³

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3 years ago
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