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inessss [21]
3 years ago
6

When did oxygen first appear in earth's atmosphere??

Chemistry
1 answer:
ad-work [718]3 years ago
7 0
<span> the atmosphere holds about 21 per cent oxygen. Over the Earth’s 4.6 billion year history, oxygen did not appear in the atmosphere until perhaps about 2.5 billion years ago. Since then, oxygen levels have fluctuated in tandem with global geological and biological events, such as mass extinctions.</span>
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What happens to the number of valence electrons as you move from left to right in the periodic table?
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Valence electrons increases
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1.-Identifica y menciona los elementos que
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Answer:

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What are 4 similarities of Metals, Nonmetals, and Metalloids?
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7 0
3 years ago
How many grams of oxygen gas (02) are needed to completely react with 9.30 moles
Luba_88 [7]

Answer:

223 g O₂

Explanation:

To find the mass of oxygen gas needed, you need to (1) convert moles Al to moles O₂ (via the mole-to-mole ratio from reaction coefficients) and then (2) convert moles O₂ to grams O₂ (via the molar mass). When writing your ratios/conversions, the desired unit should be in the numerator in order to allow for the cancellation of the previous unit. The final answer should have 3 sig figs because the given value (9.30 moles) has 3 sig figs.

4 Al + 3 O₂ ----> 2 Al₂O₃
^         ^

Molar Mass (O₂): 32.0 g/mol

9.3 moles Al          3 moles O₂              32.0 g
-------------------  x  ---------------------  x  --------------------  =  223 g O₂
                              4 moles Al               1 mole

6 0
2 years ago
_Fe2O3 + 2CO —&gt; _Fe + _CO2
soldi70 [24.7K]
<h3>Answer:</h3>

Fe₂O₃(s) + 3CO(g) → 2Fe(s) + 3CO₂(g)

<h3>Explanation:</h3>

Concept tested: Balancing of chemical equations

  • A chemical equation is balanced by putting appropriate coefficients on the products and reactants of the equation.
  • Balancing chemical equations ensures that chemical equations obey law of conservation of mass.
  • In this case; to balance the above equation we put the coefficients, 1, 3, 2, and 3 on the reactants and products.
  • Therefore; the balanced chemical equation for the reaction is;

      Fe₂O₃(s) + 3CO(g) → 2Fe(s) + 3CO₂(g)

8 0
3 years ago
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