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2 years ago

An example of a physical change is

Chemistry

2 answers:

alexdok [17]2 years ago

7 0

Answer:

A: Crushing a Rock

Explanation:

The rock is physicially being broken down and turned into either smaller pieces of rock or dust if you pound it hard enough.

aev [14]2 years ago

5 0

Answer:

the answer is a) crushing a rock because even though you broke it, its still a rock just in smaller pieces. B is not the answer because its a chemical change. The shirt is losing colour and you can't reverse it.

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The alkali earth metal beryllium (Be) engages in a chemical reaction and loses all of its valence electrons.

denpristay [2]

The loss of electron from an results in the formation of cation represented by the positive charge on the element whereas gaining of electron results in the formation of anion represented by the negative charge on the element.

The alkali earth metal beryllium ( $Be$ ) belongs to the second group of the periodic table. The ground state electronic configuration of $Be$ is: $1s^{2}2s^{2}$

From the electronic configuration it is clear that it has 2 valence electrons in its valence shell ( $2s^{2}$ ).

After losing all valence electrons that is 2 electrons from $2s$ orbital. The electronic configuration will be:

$1s^{2}2s^{0}$

Since, lose of electron is represented by positive charge on the element symbol. So, the beryllium will have +2 charge on its symbol as $Be^{2+}$ .

Hence, beryllium will have 2+ charge on it after losing all its valence electrons in the chemical reaction.

6 0

2 years ago

Read 2 more answers

Density = _____ (A)weight/length (B)mass/weight (C)mass/volume (D)volume/weight

8_murik_8 [283]

Density= Mass/Volume I am positive I just had an assignment on this

7 0

2 years ago

Read 2 more answers

How many moles of potassium nitrate, KNO3 are present in a sample with a mass of 85.2 g?

Bingel [31]

0.843 moles would be the answer

5 0

3 years ago

Which of the following reactions have a positive ΔSrxn? Check all that apply.

PolarNik [594]

Answer:

The reactions that have a positive ΔS rxn are the first and the fourth choices:

2A(g) + B(s) → 3C(g)

2A(g) + 2B(g) → 5C(g)

Explanation:

ΔS rxn is the change of entropy of the chemical reaction.

ΔS rxn = S after reaction - S before reaction.

Therefore, a positive ΔS rxn means that the entropy after the reaction is greater than the entropy before the reaction.

You may use some assumptions to predict whether a reaction will lead an increase or decrease of the entropy.

First, assume that all the non-shown conditions, such as temperature and pressure, are constant.

Under that assumption, and from the meaning of entropy as a measure of the disorder or randomness of a system you can predict the sign of the change of entropy.

2A(g) + B(s) → 3C(g)

1) The solid compounds, B(s) in this case, are very ordered and so they have low entropy.

2) Gas molecules are highly disordered (scattered), and the greater the number of molecules of the gas the larger the entropy, S).

Hence, since the product side shows 3 gas molecules and the reactant side shows 2 gas molecules and 1 solid molecule, you predict that the products have a larger entropy than the reactants, meaning an increase in entropy: ΔS rxn is positive.

2A(g) + B(g) → C(g)

Using the same reasoning, 3 gas molecules in the reactant side have more entropy than 1 molecule in the product side, and so the reaction leads to a decrease in the entropy: ΔS rxn is negative

A(g) + B(g) → C(g)

Again, 2 gas molecules in the reactant side have more entropy than 1 molecule in the product side, and so the reaction leads to a decrease in the entropy: ΔS rxn is negative

2A(g) + 2B(g) → 5C(g)

With the same reasoing, 5 molecules in the product side, lets you predict that will have more entropy than 4 molecules in the reactant side, and, the entropy will increase: ΔS rxn is positive.

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3 years ago

What is the equilibrium constant of a reaction

Svetach [21]

Homogeneous Reactions. At equilibrium, the rate of the forward and reverse reaction are equal, which is demonstrated by the arrows. The equilibrium constant, however, gives the ratio of the units (pressure or concentration) of the products to the reactants when the reaction is at equilibrium.

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3 years ago