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2 years ago

Which statement is true?

Chemistry

1 answer:

Amiraneli [1.4K]2 years ago

8 0

Answer: c. Matter and energy are conserved in chemical reactions.

Explanation:

According to the law of conservation of matter, mass can neither be created nor be destroyed. Thus the mass of products has to be equal to the mass of reactants. The number of atoms of each element has to be same on reactant and product side.

For every chemical reaction, the law of conservation of energy is applicable which states that the energy of the system remains conserved. Energy can neither be created nor destroyed. It can be transformed from one form to another.

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What happens to the composition of an atom to cause it to become positively or negatively charged?

uranmaximum [27]

It gains or loses electrons to become like the Noble gases having 8 valence electrons to become the most stable.

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3 years ago

What did Ernest Rutherford s gold foil experiment demonstrate about atoms?

mote1985 [20]

Rutherford performed gold foil experiment to understand that how negative and positive particles could Co exist in an atom. He bombarded alpha particles on a 0.00004 cm thick gold foil.

He proposed a planetary model of the atom and concluded following results and demonstrated that,
1. An atom produces a line spectrum.
2. An Electron revolves around the nucleus without any orbits.
3. Since most of the particles passed through the foil undeflected it means that most of the volume occupied by an atom is empty.
4. An Atom as a whole is neutral.
5. The deflection of few particles on the foil suggested that there is center of positive particles in an atom called the nucleus of the atom.
6. The complete rebounce of few particles on the gold foil suggested that the nucleus is very dense and hard.

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3 years ago

Which best explains how photosynthesis is helpful to humans? It reduces the amount of harmful rays released by the sun. It incre

masya89 [10]

Answer:I believe that the answer is c

Explanation: photosynthesis gives us oxygen to breath therefore it is helpful to humans

8 0

3 years ago

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What mass, in grams, of CO2 and H20 N is formed from 2.55 mol of propane?

Black_prince [1.1K]

Answer: The mass of $CO_2$ and $H_2O$ produced are 336.6 g and 183.6 g respectively.

Explanation:

The combustion reaction between propane and oxygen leads to formation of carbon dioxide and water.

Law of Conservation of mass states that the mass will remain constant for a balanced equation. This is carried out when the total number of atoms on reactant side is same as the total number of atoms on the product side. Thus the equation must be balanced.

$C_3H_8+5O_2\rightarrow 3CO_2+4H_2O$

a) 1 mol of propane produces = 3 moles of $CO_2$

Thus 2.55 mol of propane produces = $\frac{3}{1}\times 2.55=7.65 moles of [tex]CO_2$

mass of $CO_2=moles\times {\text {molar mass}}=7.65mol\times 44g/mol=336.6g$

b) 1 mol of propane produces = 4 moles of $H_2O$

Thus 2.55 mol of propane produces = $\frac{4}{1}\times 2.55=10.2 moles of [tex]H_2O$

mass of $H_2O=moles\times {\text {molar mass}}=10.2mol\times 18g/mol=183.6g$

The mass of $CO_2$ and $H_2O$ produced are 336.6 g and 183.6 g respectively.

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2 years ago

Which of the following processes are exothermic?Which of the following processes are exothermic?Br(g) + e- → Br-(g)Li(s) → Li(g)

Ksenya-84 [330]

Answer:

The correct answer is: None of the above are exothermic.

Explanation:

Energy is the ability to perform a job or to produce heat. Chemical reactions involve a rearrangement of atoms between substances with rupture or formation of chemical bonds and this generates changes in the energy of the system.

An exothermic reaction is that reaction where heat is released. This means that the energy of the molecules of the products is less than the energy of the molecules of the reactants.

An endothermic reaction is that chemical reaction that, when it occurs, consumes energy, that is, the products obtained have greater energy than the initial reagents, since they have taken part of the heat of the environment.

Sublimation is the change of state of a substance from solid to gas directly without going through the liquid state. This process requires energy to be carried out because the strong attractive energies between the solid molecules must be broken. So it is an endothermic process. This is what happens in the following reactions:

Li(s) → Li(g)

NaF(s) → Na+(g) + F-(g)

Dissociation is a process in which complexes, molecules or salts are separated into smaller molecules, ions or radicals, usually reversibly. Within the dissociation is the homolytic rupture, where each atom separates and carries the same charge of electrons. Thus free radicals are formed. To dissociate or break these bonds requires energy, so it is endothermic. This type of reaction occurs in:

Cl2(g) → 2Cl(g)

Electronic affinity is defined as the energy exchanged when an isolated and fundamental state gaseous atom takes an electron to form an anion (negative ion). When the electronic affinity is greater than zero, the process would be endothermic and when the electroaffinity is less than zero, the process would be exothermic.

This occurs in:

Br(g) + e- → Br-(g)

The highest electronic affinities are for the elements of group 17 of the periodic table, the group to which bromine belongs. This means that the electronic affinity is greater than zero and is endothermic.

The correct answer is: None of the above are exothermic.

Br(g) + e- → Br-(g) 

7 0

3 years ago

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