What indicates a chemical change?
A) Change from a liquid to a gas
B) Change in the amount of material
C) Change in the type of substance present
D) Change in the texture of a substance

The set of values that represents standard pressure and standard temperature is (3) 101.3 kPa and 0 °C.

The standard state comprehends a set of conditions that are defined by convention.

At standard pressure and temperature (STP),  1 mole of an ideal gas occupies 22.4 L.

The set of values that represents standard pressure and standard temperature is (3) 101.3 kPa and 0 °C.

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The reaction of 1.35 g of Al(s) with excess hydrochloric acid produces approximately 0.15 g of H2(g). This is determined by converting the mass of Al(s) to moles, using the balanced chemical equation to determine the equivalent moles of H2(g), and finally converting the moles of H2(g) back to grams.

The reaction given is: 2 Al(s) + 6 HCl(aq) → 2 AlCl3(aq) + 3 H2(g). This shows that for every 2 moles of Al(s), 3 moles of H2(g) are produced. First, we need to convert the mass of Al(s) to moles. The molar mass of Al is approximately 27 g/mole. So, 1.35 g of Al(s) equates to approximately 0.05 moles. In a balanced equation, the ratio of moles of Al to H2 is 2:3. Therefore, the amount of H2 generated from 0.05 moles of Al would be (0.05 * 3) / 2 = 0.075 moles. The molar mass of H2 is approximately 2 g/mole, so 0.075 moles of H2(g) equates to approximately 0.15 g. Therefore, the reaction of 1.35 g of Al(s) with excess hydrochloric acid produces approximately 0.15 g of H2(g).

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Answer:

The answer is C

Explanation:

Mendeleev’s periodic table arranged elements in order of increasing atomic mass; it was noticed that chemical properties repeated. Mendeleev predicted an element had not been discovered to fit the space.

First we find for the wavelength of the photon released due to change in energy level. We use the Rydberg equation:

1/ʎ = R [1/n1^2 – 1/n2^2]

where,

ʎ is the wavelength

R is the rydbergs constant = 1.097×10^7 m^-1

n1 is the 1st energy level = 1

n2 is the higher energy level = infinity, so 1/n2 = 0

Calculating for ʎ:

1/ʎ = 1.097×10^7 m^-1 * [1/1^2 – 0]

ʎ = 9.1158 x 10^-8 m

Then calculate the energy using Plancks equation:

E = hc/ʎ

where,

h is plancks constant = 6.626×10^−34 J s

c is speed of light = 3x10^8 m/s

E = (6.626×10^−34 J s * 3x10^8 m/s) / 9.1158 x 10^-8 m

E = 2.18 x 10^-18 J = 2.18 x 10^-21 kJ

This is still per atom, so multiply by Avogadros number = 6.022 x 10^23 atoms / mol:

E = (2.18 x 10^-21 kJ / atom) * (6.022 x 10^23 atoms / mol)

E = 1312 kJ/mol

To ionize a ground state hydrogen atom, the energy required is 1312 kJ/mol.  

Calculating the Energy Required to Ionize a Ground State Hydrogen Atom

To calculate the energy required to ionize a ground state hydrogen atom, we use the formula for the ionization energy of hydrogen. The ionization energy (">Ei") represents the energy required to remove an electron completely from an atom:

The ionization energy can be found using the Rydberg formula for hydrogen:

Ei = -13.6 eV

Since 1 electron-volt (eV) is equal to 1.602 x 10⁻¹⁹ Joules, we convert this energy to Joules:

Ei (in Joules) = -13.6 eV × 1.602 x 10⁻¹⁹ J/eV = -2.1792 x 10⁻¹⁸ J

To find the energy required per mole of hydrogen atoms, we use Avogadro's number (6.022 x 10²³ atoms/mol):

Total energy per mole

= Ei × Avogadro's number

= -2.1792 x 10⁻¹⁸ J × 6.022 x 10²³ mol⁻¹

This results in:

Total energy per mole = -1.312 x 10⁶ J/mol

Since the question asks for the energy in kilojoules:

-1.312 x 10⁶ J/mol = -1312 kJ/mol

Therefore, the energy required to ionize a ground state hydrogen atom is 1312 kJ/mol.

Hydrochloric acid has a chemical formula of HCl. Now when this is mixed with water to form an aqueous solution, HCl dissociates into its component ions:

HCl  -->  H+  +  Cl-

HCl completely dissociates into H+ and Cl- because it is a strong acid. The species that is responsible for this acidic nature is H+ ion.

Answer:

H+

The quantum mechanical model of the atom, developed from Schrödinger's wave equation, describes the probability of finding an electron in a certain position rather than defining an exact path. It utilizes orbitals to depict likely electron locations, contrasting with Niels Bohr's model of well-defined circular orbits.

The quantum mechanical model of the atom is concerned with the probability of finding an electron in a certain position. This concept is a key aspect of quantum mechanics, which posits that we cannot specify the exact location of an electron, but can only describe the probability of its presence within a certain region of space. This model is a radical departure from the Bohr model, which prescribed very well-defined circular orbits for the electron paths around the nucleus.

Erwin Schrödinger developed the Schrödinger wave equation, a mathematical formulation leading to wave functions that describe these probabilities. Unlike Niels Bohr's model that employed well-defined circular orbits for electrons, the quantum mechanical model uses orbitals, which are mathematically derived regions indicating where an electron is likely to be found.

The Bohr model was an earlier atomic theory proposed by Niels Bohr, whereas the quantum mechanical model derives from the solution to Schrödinger's equation and does not define exact electron paths but rather probability densities for electron locations. The wave functions or orbitals are three-dimensional stationary waves characterized by quantum numbers resulting from their mathematical nature, without the need for the ad hoc assumptions required in Bohr's model.

Answer: 8.1 %

Explanation:

Molecular mass of [tex]C_{14}H_{19}NO_2[/tex]  =  235 g/mol

Atomic mass of hydrogen atom = 1 g/mol

Percentage of an element in a compound:

[tex]\frac{\text{Number of atoms of element}\times \text{Atomic mass of element}}{\text{molecular mass of element}}\times 100[/tex]

Mass Percentage of hydrogen:

[tex]\frac{19\times 1g/mol}{235 g/mol}\times 100=8.1\%[/tex]

The mass percent of hydrogen in [tex]C_{14}H_{19}NO_2[/tex] is 8.1%.

Final answer:

Atoms of the same element always have the same number of protons but can have different numbers of neutrons, which leads to the formation of isotopes. Lighter elements often have a neutron-to-proton ratio close to 1:1, while heavier elements tend to have higher ratios. The chemical properties are dictated by the number of protons and electrons, not by the number of neutrons.

Explanation:

In chemistry, the relationship between the number of protons, neutrons, and electrons defines the structure of an atom's nucleus and its place in the periodic table. All atoms of the same element have the same number of protons and electrons, which accounts for the element's chemical properties. However, the number of neutrons can vary even within atoms of the same element, leading to different isotopes. Isotopes have the same number of protons but differ in their number of neutrons, affecting their atomic mass but not their chemical properties.

The neutron-to-proton ratio increases as we look at heavier elements. The lightest element, hydrogen, can have zero, one, or two neutrons while maintaining its identity as hydrogen. For heavier elements, this ratio tends to increase, and it varies from one isotope to another. For instance, isotopes of carbon can have six, seven, or eight neutrons but always have six protons.

Stable isotopes tend to have a neutron-to-proton ratio close to 1:1 for lighter elements, increasing to 1.5:1 for heavier elements. Notably, all elements with atomic numbers greater than 83 are unstable and radioactive regardless of their number of neutrons. This peninsula of stability helps define the limits of stable existence for atomic nuclei in the sea of instability where radioactive decay occurs.

ClF5 contains 42 electrons. Ten of them are bonded pair of electrons. Thirty are in lone pairs with F atoms. So accounting for 40 electrons. The remaining two electrons are left on Cl as a lone pair. So, the bond angles will be more or less equal to 90 degrees due to the extra repulsion from the delocalized lone pair. 

Final answer:

In ClF5, which exhibits a square pyramidal structure, the smallest bond angles are the Faxial-Cl-Fequatorial angles due to the lone pair on the chlorine atom, expected to be less than 90 degrees according to VSEPR theory.

Explanation:

The student's question pertains to the smallest bond angle in ClF5, assuming we are ignoring lone-pair effects. When considering the molecular geometry of ClF5, which has five bonding pairs and one lone pair of electrons, it is designated as AX5E based on VSEPR theory. The structure is square pyramidal, with a chlorine atom at the center, five fluorine atoms at the vertices, and one lone pair of electrons. Consequently, the Faxial-Cl-Fequatorial angles are typically smaller because of the presence of the lone pair on the chlorine atom, which causes the fluorine atoms in the axial positions to be slightly bent away from the lone pair.

In a perfect square pyramidal geometry (ignoring lone-pair effects), all the bond angles are 90 degrees. However, because lone pairs occupy more space than bonding pairs, when considering the lone pair, the Faxial-Cl-Fequatorial bond angles are expected to be less than 90 degrees. These would thus be the smallest bond angles in ClF5.

In a period, the atomic radius decreases as the atomic number increases because the effective nuclear charge increases from left to right in a period.

The atomic radius of an atom of an element can be described as the shortest distance between the center of the nucleus of the atom and the valence shell of the atom. An atomic radius can also be described as half the distance between two atoms of an element that are bonded together.

In general, the atomic radius of an atom decreases as we move from left to right in a period because while moving from left to right in a period, there is an increase in the effective nuclear charge of an atom. In periods, the electrons enter the same outermost shell.

In a group from top to bottom, the atomic radius of the atom increases because of the addition of a new principle shell.

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3.25 x 10^5 μg is not equal to 325 cg.

Lipids are mostly made up of carbon, hydrogen, and oxygen. Some lipids may also contain phosphorus and nitrogen but to a lesser degree. A prime example is a triglyceride, a common fat or oil, composed of glycerol and fatty acids, both of which contain carbon, hydrogen, and a small amount of oxygen.

Lipids are a group of naturally occurring molecules that include fats, waxes, sterols, fat-soluble vitamins, monoglycerides, diglycerides, triglycerides, and others. The main types of atoms that make up lipids are carbon (C), hydrogen (H), and oxygen (O). However, they contain less oxygen compared to carbohydrates. Some lipids also might include other elements such as phosphorus (P) and nitrogen (N) but to a lesser extent.

To give you a general example, a triglyceride, which is a typical fat or oil, is made from one molecule of glycerol (which contains carbon, hydrogen, and oxygen) and three fatty acids (which are chains of carbon and hydrogen, also containing a small amount of oxygen).

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The periodic table is the arrangement of the elements in the periods and groups. They are not in order as they are arranged based on their atomic numbers.

The periodic table is the classification of the elements like alkali metals, alkaline, transitions metals, noble gases, metalloids, lanthanides etc. based on the increasing atomic numbers.

The atomic number of the elements is the number of protons present in the nucleus of the elemental atom. The atomic number defines the chemical and physical properties of the element.

Therefore, elements are not in the increasing order of the atomic mass as they are arranged based on the atomic number.

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A solution with a ph less than 7 is called Acidic Solution and has a higher number of hydrogen ion than a solution with a ph greater than 7.

The pH is a measure of the amount of hydrogen ions in Solutions .

An Acidic Solution is a solution that have high concentration or amount of hydrogen ion.

The pH of acidic solution is less than 7.

A basic Solution is a solution that have low concentration of hydrogen ion.

The pH of basic Solution is greater than 7.

Solution that are neither acidic nor basic have a pH of 7.

Therefore, A solution with a ph less than 7 is called Acidic Solution and has a higher number of hydrogen ion than a solution with a ph greater than 7.

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