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miss Akunina [59]
3 years ago
7

1. According to the fossil record, the first LAND plants were most likely pine trees. moss and ferns. flowering plants. 2. Scien

tists have found fossils of pine cones, seeds, and leaves with veins. More than likely scientists would also find fossilized remains of fish. dinosaurs. mammals 3. Lots of shell fossils and no plant fossils tell us that Earth probably mostly covered with oceans and little dry land. true
Chemistry
2 answers:
Lynna [10]3 years ago
7 0

Answer:

It is true that earth was once covered with oceans and little dry land.

Explanation:

Over the course of around four billion years, the Earth's oceans have lost about a quarter of their original mass. Today the atmosphere is rich in oxygen, which reacts with both hydrogen and deuterium to recreate water, which falls back to the Earth's surface. So the vast bulk of the water on Earth is held in a closed system that prevents the planet from gradually drying out. According to the researchers,  the continents emerged relatively suddenly from an ocean that covered 95 percent of the Earth's surface. The appearance of large masses of dry land would have caused more extreme weather, changes in ocean currents and the emergence of proper seasons. In turn, these environmental changes may have led to rise in atmospheric oxygen that enabled the explosion of new life forms around 500 million years ago.

Law Incorporation [45]3 years ago
3 0

Answer:

Explanation:

`1. Moss and ferns

2.  Mammals

3. True

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Determine the enthalpy of neutralization in Joules/mmol for a solution resulting from 19 mL of 0.9 M NaOH solution and 19 mL of
Rina8888 [55]

Answer:

3.00 J/mmol

Explanation:

The temperature of the solution is increasing, so it's an endothermic reaction. The heat that is being absorbed can be calculated by:

Q = m*c*ΔT

Where m is the total mass (HCl + NaOH), c is the specific heat, and ΔT is the variation of the temperature (final - initial). Because the molarity is small, the solutions are basically water, so c = 4.184 J/g°C.

The mass is the molar mass multiplied by the number of moles (n), which is the volume multiplied by the molarity:

nHCl = 0.9 mol/L *0.019 = 0.0171 mol

nNaOH = 0.9 mol/L *0.019 = 0.0171 mol

Molar masses: HCl = 36.5 g/mol; NaOH = 40 g/mol

mHCl = 36.5*0.0171 = 0.62415 g

mNaOH = 40 * 0.0171 = 0.6840 g

m = 1.30815 g

Q = 1.30815*4.184*(37.8 - 28.8)

Q = 49.2597 J

Because the number of moles of NaOH is equal to the number of moles of HCl, and the stoichiometry of the neutralization is 1:1, they both react completely, so the enthalpy can be calculated based in any of them. The enthalpy is the heat divided by the number of moles. In mmol, n is 17.1 mmol.

ΔH = 49.2597/17.1

ΔH = 2.88 J/mmol

ΔH = 3.00 J/mmol

7 0
3 years ago
HELP PLEASE I HAVE A TEST TODAY AND I DON'T UNDERSTAND ANY OF THIS...
myrzilka [38]

Answer:

About 67 grams or 67.39 grams

Explanation:

First you would have to remember a few things:

 enthalpy to melt ice is called enthalpy of fusion.  this value is 6.02kJ/mol

  of ice  

 it takes 4.18 joules to raise 1 gram of liquid water 1 degree C

 water boils at 100 degrees C and water melts above 0 degrees C

 1 kilojoules is 1000 joules

  water's enthalpy of vaporization (steam) is 40.68 kJ/mol

  a mole of water is 18.02 grams

  we also have to assume the ice is at 0 degrees C

Step 1

Now start with your ice.  The enthalpy of fusion for ice is calculated with this formula:

q = n x ΔH    q= energy, n = moles of water, ΔH=enthalpy of fusion

Calculate how many moles of ice you have:

150g x (1 mol / 18.02 g) = 8.32 moles

Put that into the equation:

q = 8.32 mol x 6.02 = 50.09 kJ of energy to melt 150g of ice

Step 2

To raise 1 gram of water to the boiling point, it would take 4.18 joules times 100 (degrees C)  or 418 joules.

So if it takes 418 joules for just 1 gram of water, it would take 150 times that amount to raise 150g to 100 degrees C.  418 x 150 = 62,700 joules or 62.7 kilojoules.

So far you have already used 50.09 kJ to melt the ice and another 62.7 kJ to bring the water to boiling.  That's a total of 112.79 kJ.

Step 3

The final step is to see how much energy is left to vaporize the water.

Subtract the energy you used so far from what you were told you have.

265 kJ - 112.79 kJ = 152.21 kJ

Again q = mol x ΔH (vaporization)

You know you only have 152.21 kJ left so find out how many moles that will vaporize.

152.21 kJ = mol x 40.68  or   mol = 152.21 / 40.68  = 3.74 moles

This tells you that you have vaporized 3.74 moles with the energy you have left.

Convert that back to grams.

3.74 mol   x  ( 18.02 g / 1 mol ) = 67.39 grams

5 0
3 years ago
Is taking a glass of water and freezing it by placing in the freezer chemical change?
Burka [1]
Technically, no because you are not changing the chemical make up of water when you freeze it, you are only changing the state. (liquid to solid)
5 0
3 years ago
1. What is an isomer? How many possible isomers of hexane are there? What are the structural differences between these isomers?
UNO [17]
When two compounds have same molecular formula but different structural formula, they are said to be isomers of each other and this phenomenon is called as isomerism. 

Hexane has six isomers.

The isomers of hexane have a difference in their structure due to parent chain length (chain isomerism). They are also differentiated on the basis of straight chain as in n-hexane and branched chain as in remaining five. Structures along with names are shown below.

8 0
3 years ago
Describe what happened when sodium chloride (salt) was placed in water in the video What happens when stuff dissolves?"
Sonja [21]

Answer:

-

Explanation:

Water molecules pull the sodium and chloride ions apart, breaking the ionic bond that held them together. After the salt compounds are pulled apart, the sodium and chloride atoms are surrounded by water molecules, as this diagram shows. Once this happens, the salt is dissolved, resulting in a homogeneous solution.

6 0
2 years ago
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