7. D. 668 joules
8. B. 3 grams
<h3>Further explanation</h3>
Given
2 grams of water
6768 joules of energy
Required
Energy
Mass of water
Solution
The heat to change the phase can be formulated :
Q = m.Lf (melting/freezing)
Q = m.Lv (vaporization/condensation)
Lf=latent heat of fusion
Lv=latent heat of vaporization
7. phase change (ice to water)⇒Heat of fusion water=334 J/g
Q = 2 g x 334 J/g
Q = 668 J
8. phase change(water to vapor)⇒heat of vaporization water=2260 J/g
6768 J = m x 2260 J/g
m = 3 g
Explanation:
Independent variable and dependent variable
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The mass of hematite that contains 8.0×10³ kg of iron is 2.29 × 10⁴ kg.
<h3>What are iron ores?</h3>
Iron ores refers to minerals in which iron occur in combined form found in the earth's crust.
Some ores of iron include:
- hematite,
- magnetite,
- limonite, and
- siderite.
Molar mass of hematite, Fe₂O₃ = 160 g/mol
Molar mass iron = 56 g/mol
Percent mass of iron in hematite = 56/160 = 35%
The mass of hematite that contains 8.0×10³ kg of iron = 8.0 × 10³kg/0.35 = 2.29 × 10⁴ kg.
Therefore, the mass of hematite that contains 8.0×10³ kg of iron is 2.29 × 10⁴ kg.
Learn more about iron ores at: brainly.com/question/4693242
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