Chemistry College

Which of the following describes an exothermic reaction?
O A. AHt, reactants > AHf, products
B. AHF, reactants = AHf, products
O C. AHf, reactants = 0
O D. AHF, reactants < AHt, products

Answers

Answer 1

The option A describes an exothermic reaction.

i.e, ΔHt,reactant > ΔHt, product

What is exothermic reaction?

The reaction in which energy is release during the formation of reaction is called exothermic reaction.

Mathematically,

ΔHf = ΔH(product) - ΔH(reactant)

For exothermic reaction, ΔHt,reactant > ΔHt, product

So,for exothermic reaction, ΔHf is negative.

Where,

ΔHf = Enthalpy of formation of reaction

ΔH(product) = enthalpy of formation of product

ΔH(reactant) = enthalpy of formation of reactant

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Related Questions

What is the pH of 2.88*10^-5 M LiOH?

Answers

Answer: 9.46

Explanation: in LiOH solution concentration of OH- ions is 2.88·10^-5 M

And pOH = -log( 2.88·10^-5 M) = 4.54. Because PH + pOH = 14.00

Then pH = 14-4.54

CuCl2(aq) + Na3PO4(aq) =>?
Net ionic equation

Answers

If you are balancing the equation, your final one should be

Cu3(PO4)2 +6 NaCl.
The reaction is a double replacement reaction

* Urgent Bet no one knows this *

Answers

Answer: The name of the super continent that existed millions of years ago.

Explanation:

Our continents as they exist today were once joined together into a super continent known as Pangea. Over the millennia, the land masses broke off and drifted away creating the location of the continents we know today.

(つ ^‿^ )つ Hey there!

Answer → Is the second answer, The name of the super continent that existed millions of years ago.  

✨Hope this helps!✨

What is the first step in this
experiment?

Answers

Cutting the cardboard would be the first step

Answer: Cut the card borad

Explanation:

3x + 4y - 3z) - (2x - 6y + 7z)

x + 10y - 10z
x + 10y - 10z

x -10y - 10z

Answers

Answer: x + 10y - 10z is the answer

Explanation:

0.254g lead(ii)ethanoate, on adding excess K2CrO4 solution, gave 0.130g of lead(ii)chromate precipitate. what is the percentage composition of Pb in the organic salt? (O = 16, Cr = 52, Pb = 207).​

Answers

Answer:

32.8%

Explanation:

All of the Pb⁺² species precipitated as lead(II) cromate, PbCrO₄ (we know this as excess K₂CrO₄ was used).

First we convert 0.130 g of PbCrO₄ into moles, using its molar mass:

0.130 g ÷ 323 g/mol = 4.02x10⁻⁴ mol PbCrO₄

There's 1 Pb⁺² mol per PbCrO₄ mol, so in total 4.02x10⁻⁴ moles of Pb⁺² were in the ethanoate sample.

We convert those 4.02x10⁻⁴ moles of Pb into grams:

4.02x10⁻⁴ mol * 207 g/mol = 0.083 g Pb

Finally we calculate the percentage composition of Pb:

0.083 g Pb / 0.254 g salt * 100% = 32.8%

#15 need help don’t understand

Answers

I got B. Lmk if u need explanation

A barometer is used to measure air pressure.
Please select the best answer from the choices provided
Т
F

Answers

True is the correct answer.

How many grams of phosphorous is in the human skeleton if its average
weight is 11 kg and contains 58% of calcium phosphate (Ca3(PO4)2)?

Answers

I think 310.2 g/mol

hope this helps
3.10.2
I think most likely yes

Which of these items is made up of one or more molecules?
Gold
Hydrogen
Salt
Neon

Answers

2 one hope it’s right

The item that is significantly made up of one or more molecules is hydrogen. Thus, the correct option for this question is B.

What is a Molecule?

A molecule may be defined as a group of one or more atoms that are held together by numerous chemical bonds. It is the smallest particle of a substance that has all sorts of physical and chemical properties of that substance.

Among the given options, gold and neon are the elements, while salt is a compound. Hydrogen is a gas of diatomic molecules bearing the formula H2. It is colorless, tasteless, odorless, non-toxic, and highly combustible. Hydrogen in its molecular form is more common.

A hydrogen molecule is one of the simplest possible molecules which significantly consists of two protons and two electrons. These protons and electrons are remarkably held together by electrostatic forces.

Therefore, the item that is significantly made up of one or more molecules is hydrogen. Thus, the correct option for this question is B.

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What does purified water and fluorine make?

Answers

Answer:

Adding fluoride to the water supply reduces the incidence of tooth decay. Fluoride protects teeth from decay by demineralization and remineralization. Too much fluoride can lead to dental fluorosis or skeletal fluorosis, which can damage bones and joints.

Explanation:

N/A

As a raindrop falls from a cloud to the surface of Earth,
A. its speed increases due to gravity.
B. its speed increases due to air resistance,
C. it moves at a constant speed,
<
OD. it moves at a constant velocity

Answers

Answer:

The answer is C!

Explanation:

Hope it helps

Answer D

Explanation: did the quiz ψ(｀∇´)ψ

HELP PLEASE!! (100 points)
Describe what happens to particles of matter as you cool the matter to absolute zero
(OK). In your description, be sure to explain the changes in kinetic energy and
particle motion

Answers

Answer:

As you cool a matter to absolute zero, their kinetic energy reduces significantly and the molecules slows down and begins to aggregate together. ... As heat is added, the molecules gain more kinetic energy. This shown in their increase motion. When heat is withdrawn, the particles slows down hope this helped

In which atmospheric layer is the ozone layer? O stratosphere o thermosphere O mesosphere troposphere​

Answers

Answer:

The stratosphere

Explanation:

how many grams are there in 3400 moles of tetranitrogen dicarbide?

Answers

Explanation:

molar mass of tetranitrogen dicarbide S4N4= 4×32+4×14

128+56

184 g/mol

no.of moles =given mass/ molar mass

3400= given mass / 184

3400×184 =given mass.

625600 g

You have a container which has the capacity to hold 3 L water. If it already has 2.25 L water in it, how much more water in mL can you still add to fill it completely?

Answers

3-2.25 = 0.75 L
0.75 L = 750 mL

HELP NEED THIS BADLLLLY !!!!!!!!!

Answers

Answer:

2 is correct

Explanation:

My friend for you this answer

What is climate? What are three things that cause the earths climate?

Answers

Answer:

The climate has been caused by many natural factors including changes in the sun emissions from volcanoes variations in Earth's orbit and levels of carbon dioxide. Global climate change has typically occured very slowly over thousands or millions of years .The three causes of the Earth's climate are

Industrial activitiesAgricultural activitiesDeforestation

these are the causes of the Earth's climate.

Climate is a average weather in a given area for a long period of time is called a climate

maybe this might help ur question

A hot piece of copper was dropped into 155 g of water at 23.6 °C and 2,100 J of energy was transferred to the water. What is the final temperature of the water?​

Answers

Answer:

26.8 °C

Explanation:

Step 1: Given and required data

Mass of water (m): 155 gEnergy transferred to the water (Q): 2100 JInitial temperature of the water (T₂): 23.6 °CFinal temperature of the water (T₁): ? Specific heat of water (c): 4.184 J/g.°C

Step 2: Calculate the final temperature of the water

We will use the following expression.

Q = c × m × (T₂ - T₁)

T₂ = 2100 J/(4.184 J/g.°C) × 155 g + 23.6 °C = 26.8 °C

The answer is When The final temperature we (reached by both copper and also water) is 38.7 °C.  This method can also be used to determine other quantities, also it helps a lot such as the specific heat of an unknown metal. Step 1: when Given and required data is:When The Mass of water (m): 155 gWhen the Energy transferred to the water is (Q): 2100 JAfter that initial temperature of the water is (T₂): 23.6 °CNow when the Final temperature of the water is (T₁):?when The Specific heat of water (c): 4.184 J/g. °CStep 2: Now Calculate the final temperature of the water is:Now We will use the following expression is:Then follow this formula Q = c × m × (T₂ - T₁)

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Which gas will have the least collisions between its particles?

A. Helium at 20 C
B. Oxygen at -45 C
C. Carbon dioxide at 80 C
D. Argon at 265 K

Answers

AWNSER: A.


WHY: oxygen we breathe so there’s nothing too bad about oxygen carbon dioxide yes it’s kind of thick air though it won’t work so helium is the only good answer here

The gas that has the least collisions between its particle is helium at 20° C. The correct option is A.

What is collision?

Collision is a term used when two particles or object collides or clash and there is an exchange or transformation of energy between them. When a collision happens, the force is exerted on each other.

Helium is the second most abundant element present in the atmosphere. It is the lightest gas and its particle collides when there is an increase in the temperature.

Thus, the correct option is A. Helium at 20° C., regarding the collision of particles between its particles.

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What is the composition of a universal indicator?

Answers

Answer:

The main universal indicator is in the form of a solution and are thymol blue , methyl red , bromothymol blue and phenolphthalein this mixture is important because each component loses or gains protons depending upon the acidity of the solution being tested .

maybe this mighr help u

name this structure ​

Answers

Answer:

The fourth one- bromo trifluoro methane

Explanation:

Answer:

D

Explanation:

I believe the answer is the 4th option, bromo-trifluoro-methane

A 0.00215-g sample of polystyrene, a polymer composed of carbon and hydrogen, produced 0.00726 g of CO2 and 0.00148 g of H2O in a combustion analysis. What is the empirical formula for polystyrene?

Answers

Answer:

CH

Explanation:

Polystyrene is composed only by C and H.

We can calculate the number of C moles contained in the original sample mass (0.00215 g), using the produced mass of CO₂:

0.00726 g CO₂ ÷ 44 g/mol = 1.65x10⁻⁴ mol CO₂

As 1.65x10⁻⁴ moles of CO₂ were produced, in the polystyrene sample there were 1.65x10⁻⁴ moles of C.

Now we calculate how many moles of H₂O were produced:

0.00148 g H₂O ÷ 18 g/mol = 8.22x10⁻⁵ mol H₂O

The number of H moles produced is double the amount of H₂O moles, so in the polystyrene sample there were 1.64x10⁻⁴ moles of H.

The number of C and H moles are the same, this means the empirical formula is CH.

What are two things that interact that determine if there is a phase change or not HELP

Answers

Answer:

phase change always has two phases in contact during the change. melting => solid & liquid; evaporation (boiling) => liquid & vapor. If only one phase is present, then phase change is not occurring. Also, when two phases are in contact, no temperature changes occur. Only the pure phase demonstrates temperature change when measured. Example, when ice is added to water, at thermal equilibrium (temp = 0°C) the water temp will not continue to change. Only when all the ice has melted will the water temperature demonstrate a measured temperature change.

Explanation:

The number of moles of molecules in a 12.0-gram sample of Cl2 is equal too?

Answers

Answer:

0.3529moles

Explanation:

no of moles =mass ÷molar mass

molar mass =17+17

=34

12÷34

=0.3529moles

According to the mole concept, the number of moles of molecules in a 12.0-gram sample of Cl₂ is equal to 0.169  moles.

What is a mole?

Mole is defined as the unit of amount of substance . It is the quantity measure of amount of substance of how many elementary particles are present in a given substance.

It is defined as exactly 6.022×10²³ elementary entities. The elementary entity can be a molecule, atom ion depending on the type of substance. Amount of elementary entities in a mole is called as Avogadro's number.

It is widely used in chemistry as a suitable way for expressing amounts of reactants and products.For the practical purposes, mass of one mole of compound in grams is approximately equal to mass of one molecule of compound measured in Daltons. Molar mass has units of gram per mole . In case of molecules, where molar mass  in grams present in one mole  of atoms is its atomic mass.Number of moles is mass/molar mass= 12/70.90=0.169 moles.

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B) Which of these is NEVER an example of freshwater? A) Pacific Ocean B) Okefenokee Swamp Mississippi River Lake Pontchartrain.
​

Answers

Answer:

Lake pontchartrain

Explanation:

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