They first appeared in the fossil record around 66 million years ago, soon after the Cretaceous–Paleogene extinction event that eliminated about three-quarters of plant and animal species on Earth, including most dinosaurs.

Explanation:

6 0

3 years ago

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5.5x10² – 6.50x10' Express the calculation in correct significant digits

OLga [1]

Answer:

$6.15x10^2$

Explanation:

Hello!

In this case, when performing mathematical operations with numbers in scientific notation, the first step is to write them in standard notation:

550 - 65.0

Thus, the result without any significant figures-based analysis is:

615.0

However, since 550 is significant to the ones and 65.0 to the tenths, we need to round the result to the bigger significance, in this case to the ones; therefore the appropriate result would be:

615

That in scientific notation would be:

$6.15x10^2$

Best regards!

5 0

3 years ago

Use the data in the table above to calculate an approximate ΔH∘ in kilojoules for the synthesis of hydrazine from ammonia:

dmitriy555 [2]

On the left (reactant) side you have 6 N-H bonds and 1 Cl-Cl bond
On the right (product) side you have 4 N-H bonds, 1 N-N bond and 2 H-Cl bonds 

Add up the bond energies for each side (multiplying by the number of bonds) and calculate the difference for your ΔHº

7 0

3 years ago