How many π electrons are there in adenine? State which atoms contribute one electron to the π MOs and which atoms contribute two electrons?

Answer:

The Universe is constantly expanding and as it expands the stars and objects in space move farther apart, just like the points on the balloon when air is blown into it. Density and distribution of "stars" as the balloon expands because when volume increases the density will increase.

Hope this Helps

Answer:

B

Explanation:

a chemical change is making a new substance and physical change with a result in a different state of matter:)

Answer:

Examples of ROS include peroxides, superoxide, hydroxyl radical, singlet oxygen, and alpha-oxygen.

Answer:

Just count all the different elements like what elemets are in there and you have to identify the number of elemenst

Explanation:

for example H20 and a chemical for example thats two so you identofy which elelments are in there doesnt matter if thered multiple of it all its asking is what id the number of elemts there meaning like one or 2 mayne six different elements

Answer:

[tex]v=6.7\times 10^9\ mi/hr[/tex]

Explanation:

Given that,

The speed of light is 3×10⁸ m/s

We need to convert it into mi/hr.

Since, 1 mile = 1610 m

1 hour = 3600 s

So,

[tex]v=3\times 10^8\ \dfrac{m}{s}\\\\=3\times 10^8\ \dfrac{\dfrac{1}{1610}\ \text{miles}}{\dfrac{1}{3600}\ s}\\\\=6.7\times 10^9\ mi/hr[/tex]

So, the required speed of light is [tex]6.7\times 10^9\ mi/hr[/tex].

Answer:

Convection currents are caused by a temperature difference in gases and liquids. As one area becomes warmer than another the molecules have more energy and start vibrating more vigorously thus spreading out and becoming less dense. This means that the less dense parts will become more buoyant causing them to rise.

Explanation:

Answer:

Convection currents are caused by a temperature difference in gases and liquids.  

Explanation:

As one area becomes warmer than another the molecules have more energy and start vibrating more vigorously thus spreading out and becoming less dense. This means that the less dense parts will become more buoyant causing them to rise.

Answer:

No, IR should not soely be used to identify molecules

Explanation:

IR is a method that identifies the functional groups in a molecule by deducing the frequency of stretching and vibration of bonds. Each peculiar type of bond has a frequency for the vibration of each bond represented on the IR spectrum.

However, one method is never enough to identify a compound. A combination of methods must always be used to clear up ambiguities arising from overlapping IR frequencies. Also,  interpretation of the nuanced peaks of the fingerprint region in IR spectra is quite challenging and only gives a fair idea of the functional groups present in the compound.

Therefore other methods such as NMR, UV-VISIBLE etc should also be involved in the identification of compounds.

Answer:

Ammonia is moderately a base

Answer:

the density of CO2 gas at STP is 1.96 g/l.

Answer:

Evaporation is a technique used to separate out homogeneous mixtures where there is one or more dissolved salts.

Explanation:

Hope this helps :)

Answer:

I THINK it's D, I could be incorrect, however.

Explanation:

C3H8O, as it is flammable, and thus I wouldn't imagine it being a product of combustion. I could be incorrect, so take my answer with a grain of salt.

Answer:

Pumps also called transporters, are transmembrane proteins that actively move ions and/or solutes against a concentration or electrochemical gradient across biological membranes.

Answer:

23.61m/s

Explanation:

Km/hr is a unit of expressing the speed of a body. Speed is the rate of change of distance with time. Also, the same unit is applicable for expressing the velocity of a body. But to find the velocity, we must emphasize the direction of motion of the body.

Given parameter:

        85km/hr to cm/s

 Note:

         1000m  =1km

          3600s  = 1hr

 So;

      85 x

Cancelling out km and hr;

  =    85 x 0.278m/s

= 23.61m/s

Answer:

Atoms in group 2a are likely to form ions with a +2 charge because they have two valence electrons, both of which experience a very weak pull from the nucleus due to electron shielding. This causes the atoms to be easily pulled away from the nucleus, creating the +2 ions we see in nature.

Atoms in group 7a are likely to form ions with a -1 charge because they are one electron away from completing their outermost shell. The large number of protons in the middle of these atoms also causes the valence electrons to experience a stronger net force. This force also pulls strongly on the valence electrons of other atoms, causing the -1 ions we see in nature.

Answer:

b. cannot exist in optically active form

Explanation:

Stereochemistry is a branch of chemistry that involves the spatial arrangement of the atoms of molecules and studies how this affects the physical and chemical properties of such species.

The correct structure for (2R,3S)‑2,3‑dibromobutane can be seen in the image attached below. Since the compound is a meso compound due to the plane of symmetry. Thus, the compound is achiral. i.e. Compounds that are superimposable on its mirror image. The plane of symmetry is vertical inclined at 90°(i.e. perpendicular) to the page thus goes via the middle of the molecule.

Answer:

1 a

Explanation:

Answer:

A chemical reaction is the process in which atoms present in the starting substances rearrange to give new chemical combinations present in the substances formed by the reaction. These starting substances of a chemical reaction are called the reactants, and the new substances that result are called the products.

Answer:

C

Explanation:

Al=Aluminum

Mg=Magnesium

Answer:

Volume of water added = 148.4 mL

Explanation:

Given data:

Initial volume = 424 mL

Initial molarity = 0.189 M

Final molarity = 0.140 M

Volume of water added = ?

Solution:

Formula:

M₁V₁  =   M₂V₂

0.189 M×424 mL = 0.140 M×V₂

V₂ = 0.189 M×424 mL /0.140 M

V₂ = 80.136 M.mL / 0.140 M

V₂ = 572.4 mL

Final volume of solution is  572.4 mL.

Volume of water added = Final volume - initial volume

Volume of water added = 572.4 mL - 424 mL

Volume of water added = 148.4 mL

Question:

How are changes of state different from chemical change?

Answer:

Physical changes alter only the size, shape, form or matter state of a material. Water boiling, melting ice, tearing paper, freezing water and crushing a can are all examples of physical changes.

On the other hand, chemical changes are a bit different. In a chemical change, a new substance is formed.

Answer:

Chemical change happens when a substance changes they molecular structure, it often involves change in color (rusting iron), transfer of energy (copper smelting), or gas bubbling.

Changes of state is a physical change. An example is ice, it melts to create water. Water then can be freezed back to ice. Water is still H2O in both states（solid/liquid) Dissovling is another example. You can dissolve salt in water and can separate it by evaporating water and leaving the salt behind.

Explanation:

Answer:

They are plants also known as plankton and they produce about 80-85% of the world's oxygen.

Explanation:

Answer:

Explanation:

1) Pure substance: Water (found at home)

Appearance: It is homogeneous since it is a single substance that appears as liquid. Homogeneous is when the components of a substance are in a single phase

Separating technique: It's component cannot be separated by physical means

Boiling point: Water boils at 100 °C

Melting point: Water melts/freezes at 0°C

2) Pure substance: Table salt (found at home)

Appearance: It is also homogeneous as it is a single substance that is solid. Separating technique: It's component cannot be separated by physical means

Boiling point: Water boils at 1,465 °C

Melting point: Water melts/freezes at 801 °C

3) Pure substance: Butter (found at home and grocery store)

Appearance: It is homogeneous even though it contains different components

Separating technique: It's component can be separated by physical means since butter is an emulsion of fat in water. The 15% water content can be evaporated/distilled out at 100 °C

Boiling point: Butter starts boiling at about 110-120 °C

Melting point: It melts at about 37 °C

4) Pure substance: Candle (wax) (found at home and grocery store)

Appearance: It is homogeneous

Separating technique: It's component cannot be separated by physical means

Boiling point: It starts boiling around 370 °C

Melting point: It melts at about 37 °C

5) Pure substance: table sugar/sucrose (found at home, grocery stores and in supermarkets)

Appearance: It is homogeneous

Separating technique: It's component cannot be separated by physical means

Boiling point: It starts boiling around 697 °C

Melting point: It melts at about 186 °C

A pure substance is an homogeneous material, having a composition, and

properties that are consistent through out the material.

The chemical properties of a pure substance are defined, such as the

products of its reaction can be predictable.

A chemical is pure when it consist of a single type of particle such as an

element, a molecule or a compound.

The five pure substances are presented as follows;

[tex]\displaystyle\begin{tabular}{|l|l|l|l|l|}\underline{Pure \ Substances}&\underline{Appearance}&\underline{Separaing Tech}&\underline{Boiling \ Point}&\underline{Melting \ point}\\1. Diamond&Translucent \ solid&Inseparable&3550^{\circ}&4830^{\circ}\\2. Table \ salt&White\ crystals&Insepble&801^{\circ}&1413^{\circ}\\3. Water&Tran parent \ liquid&Insepble&0^{\circ}&100^{\circ}\\4. Sugar&Whilte \ crystals&Heating&Decomposes&186^{\circ}\\5. Gold&Yellowish \ metal&Inseparable& 2700^{\circ}&1064^{\circ}\end{array}[/tex]

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Answer:

b

Explanation:

this should help

Answer:

it has 12 carbon atoms and 22 hydrogen atoms and 11 oxygen atoms

Explanation:

Answer: 0.217 mol

Explanation:

To find the amount of moles in a 10 g sample, we need the molar mass of ethanol.

Molar Mass: 46.07 g/mol

Now that we have the molar mass, we can find moles.

[tex]10.0 g*\frac{1mol}{46.07g}=0.217 mol[/tex]

We know that there are 0.217 mol in a 10.0 gram sample.

Answer:

Explanation:

When volume of gas is V , pressure is P and temperature is T , if n be number of moles of gas

PV / RT = n , R is universal gas constant .

When volume becomes .5 V , pressure P and temperature T

number of moles = Px .5 V / RT = .5 PV / RT = .5 n

Number of moles of gas becomes half .

so 4 moles becomes  2 moles

No of moles lost = 4 - 2 = 2 moles.

The correct answer is Hot water increases the collision rate of molecules, causing the reaction to occur faster.

Explanation:

Temperature is directly related to the kinetic energy or movement of molecules in a substance. In this context, a higher temperature leads to more kinetic energy or more collision between molecules. At the same time, a chemical reaction involves molecules of two or more substances colliding and creating bonds to form new substances. This implies an increase in temperature means molecules colliding faster, new substances forming in a shorter time, and therefore a faster chemical reaction. According to this, the first answer is correct.