Which of the following best demonstrates the effect of static friction? A. A person pushing a couch and it slowly sliding across a floor B. A person moving a ball through a stream of water C. A person dropping a ball to the ground. D. A person pushing a couch without being able to move it

Answer:

The correct option is C

Explanation:

For a reaction to occur, there is a minimum amount of energy that must be "met". This minimum amount of energy is called activation energy. Activation energy is the minimum amount of energy required for a reaction to occur. When this activation energy is high, it takes a longer time for the reaction to occur, hence it slows down the rate of a chemical reaction but when the activation energy is low, the rate of a chemical reaction is increased.

A catalyst is known to increase the rate of a chemical reaction - it does this by reducing the activation energy of the reaction, providing an alternative reaction pathway for the reaction.

This is as straightforward as it gets. If however you need to determine how much of each product is produced, then the balanced equation is a must.

Usually, gasoline is expressed as octane in combustion reactions, which means that the balanced equation for its combustion is

2C8H18+25O2→16CO2+18H2O

But, like I've said, for the combined mass of the products all you really need to know is the combined mass of the reactants.

Addendum

Let's say you want to know exactly how much of each compound is formed. In this case, you must check for a limiting reagent. The number of moles of octane is

21⋅103 g⋅1 mole octane114.0 g=184.2 moles

The number of moles of oxygen is

85⋅103 g⋅1 mole O232.0 g=2656 moles

According to the mole ratio between these two, each 2 moles of octane need 25 moles of oxygen, so

noxygen that reacts=noctane⋅252=2303 moles , which means that octane is the limiting reagent. The actual mass of oxygen that reacts is

2303 moles⋅32.0 g1 mole=73.7 kg

This means that the combined mass of the produced water and carbond dioxide is actually

21 kg+73.7 kg=94.7 kg

85 kg−73.7 kg=11.3 kg of oxygen will not react. If you want to count this oxygen as well, the total combined mass of the products will again be 106 kg .

In complete and ideal combustion of gasoline using the principle of conservation of mass, the total combined mass of carbon dioxide and water produced when a gasoline tank holding 21 kg of gasoline burns consuming 84 kg of oxygen is 105 kg.

The subject of your question is based on the principle of conservation of mass, a fundamental concept in chemistry. The principle of conservation of mass states that the total mass of the reactants (the starting materials in a chemical reaction) is equal to the total mass of the products (the substances formed by the reaction). Hence, in the combustion (burning) of gasoline, the total combined mass of carbon dioxide and water that is produced would be equal to the sum of the masses of the gasoline and the oxygen consumed.

In your case, the total mass of gasoline and oxygen consumed is 21 kg (for gasoline) + 84 kg (for oxygen) = 105 kg. This means that given ideal condition and complete reaction, the total combined mass of carbon dioxide and water produced should be 105 kg.

Remember that this calculation assumes complete conversion of gasoline and oxygen into carbon dioxide and water, without production of other byproducts such as carbon monoxide and nitrogen oxides. Actual combustion processes may not be 100% efficient and may generate other byproducts.

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The 2p sublevel of an atom consists of three p orbitals, often denoted as [tex]\(2p_x\), \(2p_y\), and \(2p_z\)[/tex]. These p orbitals have specific relative orientations in space, which can be visualized as follows:

1. [tex]\(2p_x\)[/tex]: This orbital has a dubbell-like shape oriented along the x-axis. The lobes of the du mbbell extend in opposite directions along the x-axis, and the orbital has zero electron density in the y and z directions. In other words, it is aligned parallel to the x-axis.

2. [tex]\(2p_y\)[/tex]: This orbital is similar in shape to [tex]\(2p_x\)[/tex] but is oriented along the y-axis. It has lobes extending along the y-axis in opposite directions and zero electron density in the x and z directions, making it parallel to the y-axis.

3. [tex]\(2p_z\)[/tex]: This orbital is oriented along the z-axis. It has lobes extending along the z-axis in opposite directions and zero electron density in the x and y directions, making it parallel to the z-axis.

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Answer;

-Research and development

Scientists in research and development discover new products and processes and improve current technology.

Explanation;

Research scientists are responsible for designing, undertaking and analyzing information from controlled laboratory-based investigations, experiments and trials.

Additionally, research and development is an important means for achieving future growth and maintaining a relevant product in the market. Research may be basic research and applied research applied.  Development is when findings of a research are utilized for the production of specific products including materials, systems and methods.

The oxygen element has an electronic configuration that ends with 2s²2p⁴.

The electron configuration can describe how electrons are arranged in different energy levels of an atom of an element. In the electron configuration of an atom, the number of electrons in a particular atomic orbital is written as a superscript. For example, the electron configuration of Helium (He) is written as 1s²2s².

The principal quantum number (n) will decide the maximum number of electrons that can be filled in a shell and is determined from the term 2n², where ‘n’ is the principal quantum number.

The atomic orbitals of an atom of a lower energy level should be completely filled before filling an atomic orbital with a higher energy level.

The atomic number of the oxygen atom is 8 and the electronic configuration is 1s²2s²2p⁴. It has six electrons in its valence shell and an electronic configuration ends with 2s²2p⁴.

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Questions:

1. In how many food chains do the following animals appear? (count the # of food chains in part B)  

   hawk ___4__  earthworm ___2__   fox __6___  

    owl ___3__     snake __4___          small insects__1__

2. In how many food chains do plants (parts) appear? __all(14)__

3. List the names of the living things in this forest ecosystem that are producers. Plant parts

4. List those things that are only primary consumers. Crickets, earthworms, small insects, land snails,  rabbits, and sparrows.

5. What is another name for an animal that is only a primary consumer? Herbivore

6. List those things that are only secondary consumers. Foxes, Hawks, Owls, Robins, Snakes.

7. What is another name for an animal that is only a secondary consumer? Carnivore

8. List the consumers that eat both plants and animals. Mouse, raccoon

9. What is another name for an animal that eats both plants and animals? Omnivore

10. What would happen to the food web if all the plants were removed? Everything will die.  Explain your answer. Plants are the only organisms that can make their own food.  

11. Describe how 3 animals might be affected if owls were removed from the food chain. Rabbits, mice, and snakes will probably increase since one of their predators is gone.

12. Draw three food chains showing producers and consumers that you might see in your backyard or on your way to school. (You may use words or drawings.)  

                             grass → grasshopper → robin  

                             nut → squirrel → cat  

                             berry → bird → cat  

    (OR ANY OTHER VALID EXAMPLE)

13. Since only 10% of the energy produced by a level in a food chain is passed on to its predator, there have to be many more “prey” than “predators”.  Draw a food pyramid of the first food chain listed in Part A.  Remember that there are more producers than primary consumers, more primary consumers, and secondary consumers, etc.

            raccoon  

             mouse

             land snail    

             plant parts

14. If 2000 kcal of energy are available in the grass, how much energy would be available to the cow that eats the grass?  To the human that eats the cow?  

Assuming that all energy is used:

Since only 10% of the energy is available to the next level consumer – (.1)(2000 kcal) = 200 kcal of energy available to the cow.  For the human (.1)(200 kcal) = 20 kcal available to the human.  In other words, the human-only receives 1% of the original energy produced by the plant.

15. Which organism in this food web has the greatest influence on the ecosystem?  Justify your answer.

This is a really tough one to answer. In reality, they are all equally important, and time should be spent going over all possibilities.  Most students will guess plants since all life depends on the energy produced by plants.  The teacher should also point out that, if a top-level consumer is killed off, the organisms it eats will increase in population, which might mean that more grass will be eaten, etc.  All attempts should be made to show the interdependence of organisms in an ecosystem and to show that they are, therefore, all important.

Food web and Livings Things the Forest Eat graph    

Final answer:

The error in the electron configuration 1s2 2s2 2p6 3s2 3p5 4s2 is that it places electrons in the 4s sublevel before filling the 3d sublevel. The correct order should fill the 3d sublevel before the 4s according to the Aufbau principle.

Explanation:

The student's question is about identifying the error in the given electron configuration, which is 1s2 2s2 2p6 3s2 3p5 4s2. The error in this configuration is the arrangement of electrons in the 4s sublevel before the 3d sublevel is filled. According to the Aufbau principle, which dictates the order in which sublevels are filled based on increasing energy, after the 3p sublevel is filled, electrons should start filling the 3d sublevel before the 4s. However, in the given configuration, it incorrectly shows two electrons in the 4s sublevel before the 3d sublevel has any electrons. The correct electron configuration after 3p6 should be 3d1 before moving to 4s1 or 4s2 depending on the element in question. For example, the correct configuration for potassium (Z=19) is 1s²2s²2p63s²3p64s¹, and for calcium (Z=20), it is 1s²2s²2p63s²3p64s².

Final answer:

To find the heat produced by the combustion of 2 mol of methane gas, you use the standard enthalpies of formation. The calculated heat produced is -1630.6 kJ.

Explanation:

The question involves using the concept of enthalpy change (ΔH), specifically standard enthalpies of formation (ΔH°f), to calculate the heat produced during the combustion of methane gas (CH4).

Step-by-Step Calculation:

First, write down the balanced chemical equation for the combustion of methane:

CH4(g) + 2O2(g) → CO2(g) + 2H2O(№)

Next, apply Hess's Law using the provided ΔH°f values:

CH4(g): -74.9 kJ/mol

CO2(g): -393.5 kJ/mol

H2O(№): -285.8 kJ/mol

Calculate the total enthalpy change (ΔH) for the reaction:

ΔH = [1 mol(ΔH°f CO2) + 2 mol(ΔH°f H2O)] - [2 mol(ΔH°f CH4)]

ΔH = [1 mol(-393.5 kJ/mol) + 2 mol(-285.8 kJ/mol)] - [2 mol(-74.9 kJ/mol)]

ΔH = (-393.5 kJ - 2×285.8 kJ) - (-2×74.9 kJ)

ΔH = (-393.5 - 571.6 + 149.8) kJ

ΔH = -815.3 kJ

This is the enthalpy change for the combustion of 1 mol of methane. Since we are burning 2 mol of methane, multiply by 2:

Total ΔH = 2 × -815.3 kJ

Total ΔH = -1630.6 kJ

Therefore, the heat produced by burning 2 mol of methane gas is -1630.6 kJ.

Answer: The correct answer is Option 3 and Option 4.

Explanation:

Redox reactions are termed as the reactions in which reduction and oxidation reactions occur simultaneously.

Reduction reactions are the ones where a substance gains electrons. The oxidation state of the substance gets reduced.

Oxidation reactions are the ones where a substance looses electrons. The oxidation state of the substance is increased.

Fro the given options:

Option 1: [tex]FeS(s)+2HCl(aq.)\rightarrow H_2S(g)+FeCl_2(g)[/tex]

This reaction is a type of double displacement reaction because exchange of ions takes place.

Option 2: [tex]AgNO_3(aq.)+NaCl(aq.)\rightarrow AgCl(s)+NaNO_3[/tex]

This reaction is a type of double displacement reaction because exchange of ions takes place.

Option 3: [tex]2C_3H_6(g)+9O_2(g)\rightarrow 6CO_2(g)+6H_2O(g)[/tex]

On reactant side:

Oxidation state of Carbon = +2

Oxidation state of Oxygen = 0

On product side:

Oxidation state of Carbon = +4

Oxidation state of Oxygen = -2

Here, oxidation state of carbon is increasing from +2 to +4. Thus, it is getting oxidized and oxidation state of oxygen is getting reduced from 0 to -2. Thus, it is getting reduced.

Option 4: [tex]Fe_2O_3(s)+3CO(g)\rightarrow 2Fe(l)+3CO_2(g)[/tex]

On reactant side:

Oxidation state of Iron = +3

Oxidation state of Carbon = +2

On product side:

Oxidation state of Iron = 0

Oxidation state of Carbon = +4

Here, oxidation state of carbon is increasing from +2 to +4. Thus, it is getting oxidized and oxidation state of iron is getting reduced from +3 to 0. Thus, it is getting reduced.

Hence, the correct answer is Option 3 and Option 4.

The vapour pressure of a substance actually differs relative to the temperature. So to know which compound has the vapour pressure of 58 kilopascals at 65 degrees Celsius, we refer to standard tables of temperature vs Vapour pressure.

From the tables or graph, the answer here is:

2. ethanol

Answer: 2. Ethanol

Explanation:

Answer:

D. They must have opposite spins.

Explanation:

Two electrons in the same atomic orbital have different spins or spin number. If one electron has +1/2 spin the other electron will have -1/2 spin. In other words if one electron is spinning in the clockwise direction the other electron will be spinning in the anticlockwise direction. Two electrons in the same atomic orbital have the same principal quantum number (n), azimuthal quantum number (l) and magnetic quantum number (m).

Mendeleev identified the periodic nature of elements' chemical properties when arranged by increasing atomic mass, leading to the creation of the periodic table.

Mendeleev noticed that certain similarities in the chemical properties of elements appeared at regular intervals when the elements were arranged in order of increasing atomic mass. This pattern is referred to as periodic, analogous to other phenomena that occur at regular intervals, such as the swing of a pendulum or the orbit of the moon around Earth. In the construction of his periodic table, Mendeleev even listed some elements out of atomic mass order so that they would be grouped with those that had similar chemical properties, such as tellurium (Te) being placed before iodine (I) based on properties rather than atomic mass.

Dimitri Mendeleev and Lothar Meyer independently recognized the periodic relationship among the elemental properties. While Meyer arranged elements by increasing atomic mass, Mendeleev's approach distinguished him by predicting undiscovered elements like gallium and germanium, which were later found and confirmed the utility of Mendeleev's table. This foresight helped solidify the significance of Mendeleev's work on the development of the periodic table.

Answer is: cooling.

Cooling is change from liquids to solids.

Another example is crystalisation, many elements and compounds form crystals.

A physical change occurs when a substance changes phase.

Physical property can be observed and measured without any changes in molecular composition. The same substance is present before and after the change.

The potential energy of a gas decreases during a phase change, such as cooling and condensing to a liquid.

The potential energy of a gas decreases during a phase change when a large amount of energy is extracted from the system and causes a decrease in the gas's volume, pressure, or both. For example, when a gas is cooled and condenses to a liquid, its potential energy decreases. This is illustrated by a graph of pressure vs. temperature, where the pressure of a gas continually decreases as it is cooled at a constant volume.

Answer: Option (C) is the correct answer.

Explanation:

An electrolyte is defined as the substance which when dissolved in water dissociates into ions and it is able to conduct electricity.

Ionic compounds are the compounds which are soluble in water as ;like dissolves like.

Hence, water being a polar solvent is able to dissolve ionic compounds.

Sodium bromide and calcium hydroxide are ionic compounds. So, they act as an electrolyte as they dissociate into ions in water.

Whereas magnesium sulfate is also soluble in water as solubility of sulfates of group 2A decreases down the group.

On the other hand, [tex]CCl_{4}[/tex] is a non-polar compound. Hence, it will not dissociate into ions when dissolved in water.

Thus, we can conclude that carbon tetrachloride compound is a non-electrolyte.

Nonelectrolytes are compounds that, when dissolved in an aqueous solution, do not take on any particular ionic form. Solutions without electrolytes do not conduct electricity. Here carbon tetrachloride is a non-electrolyte. The correct option is C.

Chemical substances known as nonelectrolytes are those that do not ionize at all when placed in solution. Therefore, solutions devoid of electrolytes do not conduct electricity. Covalent bonds, as opposed to ionic ones, are typically used to hold together nonelectrolytes.

Sodium bromide and calcium hydroxide are ionic compounds. So, they act as an electrolyte as they dissociate into ions in water whereas magnesium sulfate is also soluble in water CCl₄  is a non-polar compound. Hence, it will not dissociate into ions when dissolved in water.

Thus the correct option is C.

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 The   mass  of each  elements   in  chromite is as below

Fe  =24.9 %

Cr  =46.5%

O = 28.6%

calculation

percent  mass  =  atomic mass  of  element / atomic mass of FeCr2O4 x 100

from  periodic table  the atomic mass  for  Fe  = 55.85 g/mol,

Cr =52 g/mol  since  they  are two  atoms  in FeCr2O4 =  2 x 52 = 104 g/mol

for  O  = 16   since  they are two  atoms in FeCr2O4 =  16  x4  =  64  g/mol

Atomic mass for  FeCr2O4  is  = 55.85 +104+  64  = 223.85  g/mol

Percent  mass  for Fe  =55.85 /223.85  x100  = 24.9 %

                          for  Cr =  104 / 223.85  x 100  = 46.5%

                           For 0  =  64/223.85  x 100  =  28.6%

Explanation:

Coefficients are the number present in front of an atom or molecule in a chemical reaction.

For example, [tex]2Na + Cl_{2} \rightarrow 2NaCl[/tex]

In this reaction 2 in front of Na in reactant side shows 2 moles of sodium atoms are participating. Whereas 2 in front of NaCl in product side shows that 2 moles of sodium chloride is formed.

Therefore, we can conclude that coefficients in a balanced chemical equation tell you the moles of each substance involved in the reaction.

If volume is halved and temperature increased as per your question, the pressure would likely rise. Boyle's law suggests a pressure increase due to the volume reduction, and Charles's law predicts further pressure escalation with the temperature augmentation. However, the specifics of the final pressure would require more information on the gas's details.

Your question asks what would happen to the pressure if the volume were reduced to 0.5 liters and the temperature were increased to 260 degrees Celsius. To answer, we can reference the ideal gas law and Charles's law, both concepts from physics.

Charles's law states that at constant pressure, the volume of a gas is directly proportional to its absolute temperature. However, your question involves changes in both volume and temperature, which requires application of the ideal gas law (PV = NkT). This equation suggests an inverse relationship between volume and pressure when the number of molecules (N) and temperature (T) are constant.

Per the question, the volume is halved and the temperature is increased, which complicates the pressure outcome. Boyle's law anticipates that halving the volume under constant temperature would double the pressure. If we consider the temperature increase, Charles's law would suggest that the enlarged thermal energy of the gas would further increase the pressure.

Finally, pressure is also contingent on the number of gas molecules. If the original density was halved without a loss of molecules, your volume would need to double, not halve. This inconsistency suggests the presence of additional influencing factors, perhaps a change in the gas's composition or quantity, or a misunderstanding in the question.

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