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Mila [183]
3 years ago
7

Which statement best describes a chemical change?

Chemistry
2 answers:
Reika [66]3 years ago
7 0
A. A substance changes size or phase.
valentinak56 [21]3 years ago
4 0
D is probably your best bet, at least from what I know.
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Water is 11% hydrogen and 89% oxygen by mass. How many grams of oxygen are in a 250 g glass of water?
mylen [45]

Answer:

mass O2 = 222.5 g

Explanation:

  • %wt = ((mass compound)/(mass sln))×100

balance reaction:

  • 2H2 + O2 ↔ 2H2O

∴ %wt H2 = 11 % = ((mass H2)/(mass H2O))×100

∴ %wt O2 = 89 % = ((mass O2)/(mass H2O))×100

∴ mass H2O 250 g

⇒ mass O2 = (0.89)(250 g)

⇒ mass O2 = 222.5 g

3 0
4 years ago
What is the approximate age of the oldest fossils of early human ancestors?
Vesna [10]

Answer:approx 300,000 years ago

Explanation:

Fossils attributed to H. sapiens, along with stone tools, dated to approximately 300,000 years ago, found at Jebel Irhoud, Morocco yield the earliest fossil evidence for anatomically modern Homo sapiens

7 0
3 years ago
Read 2 more answers
Which of the following statements is true?
natita [175]

Answer:

b

Explanation:

5 0
3 years ago
Ab cd and Ef intersect at p. If r=90, s=50, t=60, u= 45 and w=50, what is the value of x?
ziro4ka [17]

Answer:

8

Explanation:

3 0
3 years ago
17. Consider the reaction shown and identify the statement that is not true.
Crazy boy [7]

Answer: Water must be present for this reaction to occur.

Explanation:

Decomposition reactions require breaking of bonds which require energy and thus all of the decomposition reactions are endothermic reactions.

The salts which are soluble in water are designated by symbol (aq) and those which are insoluble in water and remain in solid form are represented by (s) whereas liquids are represented by (l) and gases are represented by (g) after their chemical formulas.

The balanced chemical reaction of CaCO_3 decomposition is:

CaCO_3(s)\rightarrow CaO(s)+CO_2(g)

The decomposition of CaCO_3 requires heat and leads to formation of CaO as solid and CO_2 as product.

Thus the the statement that is not true is Water must be present for this reaction to occur.

6 0
4 years ago
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