1answer.
Ask question
Login Signup
Ask question
All categories
  • English
  • Mathematics
  • Social Studies
  • Business
  • History
  • Health
  • Geography
  • Biology
  • Physics
  • Chemistry
  • Computers and Technology
  • Arts
  • World Languages
  • Spanish
  • French
  • German
  • Advanced Placement (AP)
  • SAT
  • Medicine
  • Law
  • Engineering
Dahasolnce [82]
3 years ago
15

You break a pencil lead. Which statement is true?

Chemistry
1 answer:
aalyn [17]3 years ago
7 0

Answer:

  • <em><u>A physical change has occurred, with no energy change.</u></em>

Explanation:

When a pencil lead is broken there is not change of any chemical properties, therefore it is not a chemical change, but just a physical change. In this case the change is just the number of pieces and dimensions.

Chemical changes always involve the formation of new different substances; the bonds between the atoms of the starting substances (reactants) breake and new bonds are formed leading to new substances (products) with different chemical composition (arrange of atoms). Chemical changes occur through chemical reactions.

Hence, if there is not change on the chemical composition, you think on physical changes. Physical changes include change in shape, size, state of matter (e.g. solid, liquid, gas). In the case of a pencil lead breaking, it is a change in shape and size.

Also, since energy has not been absorbed or released during the change, the energy of the pencil lead before having been broken is equal to the sum of the energies of the pieces of pencil lead obtained. So, this is a physical change with no energy changes.

Some examples of physical changes that include change in energy are the change of state (e.g. solid to liquid or liquid to gas) and the dissolution of a compound.

You might be interested in
Oxygen gas generated in an experiment is collected at 25.0°C in a bottle inverted in a trough of water. The total pressure is 1.
Nitella [24]

Answer:

0.007 mol

Explanation:

We can solve this problem using the ideal gas law:

PV = nRT

where P is the total pressure, V is the volume, R the gas constant, T is the temperature and n is the number of moles we are seeking.

Keep in mind that when  we collect a gas over water we have to correct for the vapor pressure of water at  the temperature in the experiment.

Ptotal = PH₂O + PO₂  ⇒ PO₂ = Ptotal - PH₂O

Since R constant has unit of Latm/Kmol we have to convert to the proper unit the volume and temperature.

P H₂O = 23.8 mmHg x 1 atm/760 mmHg =  0.031 atm

V = 1750 mL x 1 L/ 1000 mL = 0.175 L

T = (25 + 273) K = 298 K

PO₂ = 1 atm - 0.031 atm = 0.969 atm

n =  PV/RT = 0.969 atm x  0.1750 L / (0.08205 Latm/Kmol x 298 K)

n = 0.007 mol

6 0
2 years ago
Which of these observations helped Rutherford determine that atoms have tiny, dense, positively charged nuclei?
gladu [14]
The third reason helped Rutherford to discover the nucleus.
5 0
3 years ago
When did the water level in Lake Mead become a concern?
xenn [34]

Answer:

in 1983, Lake Mead had a recorded water level of 1,225 feet above sea level. The closest it's been to that level in modern times was in 2000. Explanation:

6 0
2 years ago
opper(I) ions in aqueous solution react with NH 3 ( aq ) according to Cu + ( aq ) + 2 NH 3 ( aq ) ⟶ Cu ( NH 3 ) + 2 ( aq ) K f =
Y_Kistochka [10]

Answer:

55.373g/l

Explanation:

The dissolved amount of sparingly soluble salts is interlinked with a unitlesss quantity called as solubility product. It is a fixed quantity that only increases with the rise in temperatures and is used to predict the salting out of compounds. If the value of ionic product (Q) is larger than (Ksp), precipitation of compound occurs.

Given:

The solubility product of CuBr is 6.3×10−9.

The concentration of NH3 is 0.10 M.

Formula and Calculations:

The dissolution reaction (I) of CuBr is shown below.

The reaction showing dissolution of CuBr in NH3 is shown below.

The above reaction can be obtained by adding reaction (I) and (II) as shown below.

The equilibrium constants will get multiplied.

Suppose the solubility of CuBr is “s”.

It is given that concentration of NH3 is 0.10 M.

The equilibrium constant expression for the above reaction is as follows,

Here,

The concentration of pure solids is 1 M. Thus, the concentration of CuBr is 1 M.

As calculated, the value of Ksp is 396.9.

Substitute all the required values in above formula.  

On further solving above equation,

Therefore, the solubility of CuBr in ammonia is 0.386 M.

The formula to calculate solubility

Solubuility (g/l)= Molarity(M) x Molarmass

Chemistry homework question answer, step 2, image 10

The molar mass of CuBr is 143.45 g/mol.

The formula to calculate solubility in g/L is given below.

The molar mass of CuBr is 143.45 g/mol.

therefore,

solubility = 0.386M x 143.45g/mol

where (M = mol/l)

solubility = 55.375g/l

5 0
2 years ago
Determine the value of the equilibrium constant, Kgoal, for the reaction C(s)+12O2(g)+H2(g)⇌12CH3OH(g)+12CO(g), Kgoal=? by makin
Licemer1 [7]

Answer:

1.71x10²⁷

Explanation:

If we sum 1/2 of (3) + 1/2 of (1):

1/2 (3.) C(s) + 1/2O₂(g) ⇌ CO(g), K₃ = √2.10×10⁴⁷  = 4.58x10²³

1/2 (1)   1/2CO₂(g) + 3/2H₂(g) ⇌ 1/2CH₃OH(g) + 1/2H₂O(g), K₁ = √1.40×10² = 11.8

C(s) + 1/2O₂(g) +<u> 1/2CO₂(g) </u>+<u> 3/2H₂(g</u>) ⇌ 1/2CH₃OH(g) + <u>1/2H₂O(g)</u> + <u>CO(g)</u>

K' = 4.58x10²³ * 11.8 = 5.42x10²⁴

+1/2 (2):

<u>1/2 CO(g)</u> +<u> 1/2H₂O(g)</u> ⇌<u> 1/2CO₂(g)</u> + <u>1/2H₂</u> (g), K = √1.00×10⁵ = 316.2

C(s) + 1/2O₂(g) + H₂(g) ⇌ 1/2 CHO₃H(g) + 1/2CO(g)

K'' = 5.42x10²⁴* 316.2 =

<h3>1.71x10²⁷</h3>

5 0
3 years ago
Other questions:
  • A ray of yellow light has a wavelength of about 5.8×10−7 m. Will exposure to yellow light cause electrons to be emitted from ces
    6·1 answer
  • 2. Convert 6.578 x 1023 atoms of magnesium to moles.<br> 6.578 x 1023 atoms x<br> mol<br> atoms
    14·1 answer
  • Water exists in liquid form between its 1. Freezing and Boiling point 2. Freezing and melting point 3. Boiling and melting point
    14·1 answer
  • A volcano ejects a glowing chunk of lava straight up.
    12·1 answer
  • Classify each of the following as a pure substance or a mixture; if it is a mixture, state whether it is heterogeneous
    12·1 answer
  • Is the equation above balanced or unbalanced? Explain? Worth 55 points.
    5·2 answers
  • What is a force, provide an example
    13·1 answer
  • Plsss helpppp!!!!!!!!!!!!!!!​
    6·1 answer
  • What is the name of the family with an oxidation number of +2?
    11·2 answers
  • What conversion factors<br> determine the number of<br> molecules from the mass of a<br> compound?
    13·1 answer
Add answer
Login
Not registered? Fast signup
Signup
Login Signup
Ask question!