CHEMISTRY HIGH SCHOOL

18. Which of the following reactions are endothermic or exothermic? Explain your answers. A. When a certain amount of potassium nitrate is dissolved in water, the water temperature drops from 23°C to 18°C. B. Jack cooks himself a steak. C. When cold water is mixed with sulphuric acid, the mixture can rapidly reach the boiling point of water. D. A flare burns up slowly.

Answers

Answer 1

Answer:

Answer:

The answer to your question is below

Explanation:

An endothermic reaction absorbs heat to proceed.

An exothermic reaction releases heat to proceed.

A. When a certain amount of potassium nitrate is dissolved in water, the water temperature drops from 23°C to 18°C. This is an example of an endothermic reaction because of the temperature diminishes.

B. Jack cooks himself a steak. This is an endothermic reaction because the steak does not cook itself it needs heat to be cooked.

C. When cold water is mixed with sulphuric acid, the mixture can rapidly reach the boiling point of water. This is an exothermic reaction because the temperature of water increases, which means that energy is been released.

D. A flare burns up slowly. I think it is an endothermic reaction because it was supply energy to proceed.

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the empirical formula of a compound is NO2. it's molecular mass is 92g/mol. What is its molecular formula?

Answers

The molecular formula:
$N_x(O_2)_x$

$M_(N_x(O_2)_x)=x * M_N + x * 2 * M_O \n \nm_N=14 \ (g)/(mol) \nm_O=16 \ (g)/(mol) \n M_(N_x(O_2)_x)=92 \ (g)/(mol) \n \n92=x * 14+x * 2 * 16 \n92=14x+32x \n92=46x \n(92)/(46)=x \nx=2 \n \nN_2(O_2)_2 \Rightarrow N_2O_4$

The molecular formula is N₂O₄.

The chemical symbol for sodium is
a. Sn.
b. N.
c. S.
d. Na.

Answers

For this question the answer would be D. Na is the chemical symbol for sodium.

The answer would be D.

The type of reaction that takes place when one element reacts with a compound to form a new compound and a different element is a ____a. combination reaction.
b. decomposition reaction.
c. single-replacement reaction.
d. double-replacement reaction.

Answers

Answer: c. single-replacement reaction.

Explanation:

Combination is a chemical reaction in which two or more than two substances combine to form a single product.

$A+B\rightarrow AB$

Decomposition is a chemical reaction in which one substance decompose to form two or more than two products.

$AB\rightarrow A+B$

A single replacement is a chemical reaction in which a more reactive element displaces a less reactive element from its salt solution, thus one element reacts with a compound to form a new compound and a different element.

$A+BC\rightarrow B+AC$

Double displacement is a chemical reaction in which ion exchange takes place.

$AB+CD\rightarrow AD+BC$

C. single replacement. A single replacement is represented by this formula : AB + C = AC + B

According to one acid-base theory, a water molecule acts as a base when it accepts(1) an H+ ion (3) a neutron
(2) an OH- ion (4) an electron

Answers

Answer : The correct option is, (1) an $H^+$ ion

Explanation :

According to the Bronsted-Lowry or acid-base concept, a substance is called as an acid if it can donate a proton and a substance is called as a base if it can accept a proton. And the substance may be a molecule or an ion.

When a water molecule acts as an acid then it can donate a proton or $H^+$ ion.

When a water molecule acts as a base then it can accepts a proton or $H^+$ ion.

Hence, the correct option is, (1) an $H^+$ ion

Final answer:

In accordance to the Brønsted-Lowry theory, a water molecule acts as a base when it accepts an H+ ion during the ionization of water. This capability for water to function both as an acid when donating an H+ ion, and a base when accepting an H+ ion makes it amphoteric.

Explanation:

According to the Brønsted-Lowry theory of acids and bases in Chemistry, a water molecule acts as a base when it accepts an H+ ion. This occurs during the ionization of water, a chemical reaction that takes place when water auto-ionizes into a hydronium ion (H3O+) and a hydroxide ion (OH-). Therefore, the correct choice from your options is (1) an H+ ion.

Water acts as an acid when it donates an H+ ion and as a base when it accepts an H+ ion, transforming it into a hydronium ion. This capacity for water to act as both an acid and a base makes it amphoteric.

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Determine the number of moles 28.8 g Br2

Answers

well, you would just divide 28.8 by the molar mass of Br2 (the gram amount on the periodic table x2 because there's two of them)

What is the percent by mass of chlorine in NaCl?

Answers

The percent by mass of chlorine in NaCl is 60.68 % of chlorine

calculation

mass % of chlorine =mass of chlorine /mass of NaCl x 100

from periodic table the mass of cl= 35.5 g/mol

that of of Na = 23 g/mol

The mass of NaCl is therefore = 35.5 g/mol + 23 g/mol =58.5 g/mol

mass % is therefore= (35.5 / 58.5 x 100) =60.68 %

In the given question, 60.66% is the percent by mass of chlorine in NaCl.

Mass is a physical property of matter that measures the amount of substance in an object. It is typically measured in grams (g) or kilograms (kg).

The molar mass of NaCl is 58.44 g/mol. The molar mass of chlorine is 35.45 g/mol. The formula of NaCl indicates that there is one chlorine atom for every sodium atom. Therefore, the mass of chlorine in NaCl is 35.45 g/mol.

To calculate the percent by mass of chlorine in NaCl, we need to divide the mass of chlorine by the total mass of NaCl and multiply by 100. This can be expressed as follows:

Percent by mass of chlorine = (mass of chlorine/mass of NaCl) × 100

Substituting the values, we get:

Percent by mass of chlorine = (35.45 g/mol/58.44 g/mol) × 100

= 60.66%

Therefore, the percent by mass of chlorine in NaCl is 60.66%.

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