Answer:
Egypt
Explanation:
Hi again
What kind of atoms An attachment
Two samples of sodium chloride with different masses were decomposed into their constituent elements. One sample produced 2.55 g of sodium and 3.93 g of chlorine. Being consistent with the law of constant composition, also called the law of definite proportions or law of definite composition, which set of masses could be the result of the decomposition of the other sample
Answer:
4.71 g of sodium and 7.25 g of chlorine
Explanation:
Note: The question is incomplete. the complete question is given below:
Two samples of sodium chloride with different masses were decomposed into their constituent elements. One sample produced 2.55 g of sodium and 3.93 g of chlorine. Being consistent with the law of constant composition, also called the law of definite proportions or law of definite composition, which set of masses could be the result of the decomposition of the other sample?
4.71 g of sodium and 3.30 g of chlorine
4.71 g of sodium and 7.25 g of chlorine
4.71 g of sodium and 1.31 g of chlorine
4.71 g of sodium and 13.7 g of chlorine
The law of definite proportions states that all pure samples of a particular chemical compound contain the same elements combined in the same proportion by mass.
This means that irrespective of the source of any sample of a pure chemical compound, the constituents elements are always combined in the same mass ratio.
In the first sample, the mass ratio of Sodium to chlorine is given below:
mass of sodium = 2.55 g
mass of chlorine = 3.93 g
mass ratio; sodium to chlorine = 2.55 / 3.93 = 0.65
From the set of masses give above, we can determine the result of the decomposition of the second sample.
4.71 g of sodium and 3.30 g of chlorine
mass ratio; sodium to chlorine = 4.71 / 3.30 = 1.43
4.71 g of sodium and 7.25 g of chlorine
mass ratio; sodium to chlorine = 4.71 / 7.25 = 0.65
4.71 g of sodium and 1.31 g of chlorine
mass ratio; sodium to chlorine = 4.71 / 1.31 = 3.59
4.71 g of sodium and 13.7 g of chlorine
mass ratio; sodium to chlorine = 4.71 / 13.7 = 0.34
From the results above, the correct set of masses for the second sample is 4.71 g of sodium and 7.25 g of chlorine
Electrons have what charge?
Answer:
negative charge
Explanation:
protons have a positive, nuetrons have a neutral charge , and electrons have a negative.
How can simple machines make work easier?
A) By decreasing the effort needed to do the work
B) By adding more work on the object
C) By increasing the friction between the machine and the object
D) By removing the force of gravity on the object
Answer:
A) By decreasing the effort needed to do the work
Explanation:
The answer fam is....... A) By decreasing the effort needed to do the work
Hence the word simple Machine
Which process is MOST similar to the development of fossil fuels?
Answer:
after millions of years underground the compounds that make up plankton and plants turn into fossil fuels Franklin decomposes into natural gas and oil white plants become cal today humans extract these resources through coal mining and the drilling of Oil and Gas Wells on land and Offshore
How many grams of sodium chloride should you theoretically produce if you start with 5.00 grams of calcium chloride and excess sodium carbonate? (answer in numbers only - no units or words)
Answer:
5.27 g of NaCl
Explanation:
The balanced equation for the reaction is given below:
Na₂CO₃ + CaCl₂ —> 2NaCl + CaCO₃
Next, we shall determine the mass of CaCl₂ that reacted and the mass of NaCl produced from the balanced equation. This can be obtained as follow:
Molar mass of CaCl₂ = 40 + (35.5×2)
= 40 + 71
= 111 g/mol
Mass of CaCl₂ from the balanced equation = 1 × 111 = 111 g
Molar mass of NaCl = 23 + 35.5
= 58.5 g/mol
Mass of NaCl from the balanced equation = 2 × 58.5 = 117 g
Summary:
From the balanced equation above,
111 g of CaCl₂ reacted to produce 117 g of NaCl.
Finally, we shall determine the theoretical yield of NaCl. This can be obtained as follow:
From the balanced equation above,
111 g of CaCl₂ reacted to produce 117 g of NaCl.
Therefore, 5 g of CaCl₂ will react to produce = (5 × 117)/111 = 5.27 g of NaCl.
Thus, the theoretical yield of NaCl is 5.27 g.
Identify the true statements about surface tension. Molecules along the surface of a liquid behave differently than those in the bulk liquid. Water forming a droplet as it falls from a faucet is a primary example of surface tension. Surface tension increases as the temperature of the liquid rises. Cohesive forces attract the molecules of the liquid to one another. Mercury has a lower surface tension than water.
Answer:
Molecules along the surface of a liquid behave differently than those in the bulk liquid.
Cohesive forces attract the molecules of the liquid to one another.
Water forming a droplet as it falls from a faucet is a primary example of surface tension.
Explanation:
Surface tension is the force that stretches the liquid surface. This force acts normal to the surface. It is the downward force that acts on the surface of the liquids which is due to the cohesive forces of the liquids.
The water molecules are bonded by a strong hydrogen bond force which is between hydrogen atom and the electronegative oxygen atom. At the surface the water molecules are attracted strongly by other water molecules which lies below the surface and are stretched at the surface. Thus the water molecules at the surface acts differently than in the bulk liquid.
Mercury have a strong cohesive force than the water and have a higher surface tension force than the water.
Surface water acquires minimum surface area, hence acquiring spherical shape of water.
How many moles are there in 3.4*10^26 moles of Ag
Answer:
It would be 151.832775 because one mole is 44.0095*3.45 i hope this helps!
Explanation:
If 9.5 × 10²⁵ molecules of CO₂ are produced in a combustion reaction, what is the mass in kg of CO₂ that is produced?
Answer:
6.9428 kg of CO2
Explanation:
1) Use Avogadro's number that states 1 mole = 6.022 x 10^23 particles. Convert 9.5 x 10^25 molecules into moles.
9.5 x 10^25 CO2 molecules[tex]x\frac{1 mole CO2}{6.022 x 10^23}[/tex] = 157.75 moles CO2
2) Convert 157.75 moles of CO2 into grams. CO2's molar mass is 44.01g.
[tex]157.75moles CO2[/tex] [tex]x \frac{44.01g/mol}{1 mole CO2}[/tex] = 6942.79g
3) Convert 6942.79 grams into kilograms (divide by 1000):
6.9428 kg
An example of electrical energy is the battery from your cell phone
Answer/Explanation:
This electrical energy now travels through the phone supplying the phone with electricity. Batteries in a cell phone supply chemical energy to electric charges. The electric charges use the energy to be put into motion.
Tetrahydrocannabinol can be nitrated with nitric and sulfuric acids to produce a nitrated derivative. Identify the most likely position of nitration on the aromatic ring, assuming no side reactions occur. Write a detailed mechanism for this transformation. Show generation of the electrophile.
Why is observational evidence important in an experiment?
Answer:
Observational evidence is essential for investigating the way disease affects populations, the patterns and distribution of risk within them, and the emergence of trends in health and disease over time.
Answer:
It tests a prediction It supports the results. It asks a testable question It predicts what will happen
Explanation:
The circuit below is powered by a 20-volt battery. What current is flowing through the on/off switch (when it is on, as shown)?
Answer:
The answer is "0.38 A".
Explanation:
Please find the missing image file in the attachment.
In the given image let:
[tex]R_{12} =R_1+R_2=16 \ \Omega \\\\R_{34} =R_3+R_4=20 \ \Omega \\[/tex]
[tex]R_P=\frac{R_{12} \cdot R_{34}}{R_{12} +R_{34}}[/tex]
[tex]= \frac{16 \cdot 20 }{16 +20}\\\\= \frac{320 }{36}\\\\= \frac{80 }{9}\\\\= 8.88 \ \Omega[/tex]
similarly,
[tex]R_{eq} =R_p+R_5+R_6\\\\[/tex]
[tex]=8.88+24+20\\\\=52.89 \ \Omega \\\\[/tex]
calculating the current value through a switch:
[tex]\to I=\frac{V}{R_{eq}} = \frac{20 \ v}{52.89 \Omega }=0.38\ A[/tex]
Answer:
D. 0.38 amperes
Explanation:
Got it correct on Gizmos
Gizmos explanation: This compound circuit contains two parallel branches connected in series to 2 more resistors. Each parallel branch contains 2 resistors in series. The resistance of the first branch is 5+11=16 ohms, and the resistance of the second branch is 20 ohms. Using the equivalent resistance formula, the resistance of this section is
1R=116+120=580+480=980
So R is 809, or 8.89 ohms. This is connected in series to a 24-ohm and a 20-ohm resistor, for a total resistance of 52.89 ohms. The battery voltage is 20 volts, so by Ohm's law
I=VR
I=2052.89=0.38amperes
A sample of N2O4(g) is placed in an empty cylinder at a certain temperature. It is allowed to decompose and form NO2(g). At equilibrium, the flask has a total pressure of 1.000 atm. If the KP at this temperature is 0.85, calculate the partial pressure (in atm) of NO2(g) at equilibrium. g
Answer:
Part. press. NO₂ in equilibrium is 0.590 atm
Explanation:
First of all, we determine the equilibrium:
N₂O₄ (g) ⇄ 2NO₂ (g)
These is a system of two unknown values.
In the begining we have x pressure of N₂O₄ and no value for NO₂.
During the reaction, y pressure has been released from N₂O₄. As ratio is 1:2, 2y will be the value for the pressure of NO₂. So in the equilibrium we have:
N₂O₄ → x - y
NO₂ → 2y
Data from the excersise states that the total pressure is 1 atm so we know that the sum of partial pressures in a mixture, will be the total one. In the equilibrium, total pressure will be:
(x-y) + 2y = 1 atm
x + y = 1 atm
Let's make the expression for Kp
Kp = [Partial pressure NO₂]² / [ Partial pressure N₂O₄]
Kp = (2y)² / (x-y)
Kp = 4y² / (x-y)
We split the x value in the first equation:
x + y = 1 atm
x = 1 atm - y
x = 1 - y → we put this in the Kp expression
0.85 = 4y² / ( 1 - y - y)
0.85 = 4y² / 1 -2y
This is a quadractic equation
0.85 - 1.7y - 4y² = 0 where (a = -4, b = -1.7 c = 0.85)
(-b +- √(b² - 4ac)) / (2a)
(1.7 +-√((-1.7)² - 4 (-4) . 0.85) / 2 .(-4) → 0.295 = y
As [ Part. press. NO₂] in equilibrium is 2y → 0.295 . 2 = 0.590 atm
Based on the total pressure at equilibrium, the partial pressure NO₂ of at equilibrium is 0.590 atm.
What are the partial pressures of the gasses at equilibrium?From the equation of the reaction, the equilibrium is determined:
N₂O₄ (g) ⇄ 2NO₂ (g)At equilibrium, N₂O₄ and NO₂ exist in the ratio 1 : 2.
N₂O₄ at x pressure releases y pressure to form NO₂ .
Thus at equilibrium:
N₂O₄ → x - y
NO₂ → 2y
Ptotal = 1 atm
Thus:
(x-y) + 2y = 1 atm
x + y = 1 atm
Also, Kp = 0.85
From the equation of the reaction:
Kp = [Partial pressure NO₂]² / [ Partial pressure N₂O₄]
Kp = (2y)² / (x-y)
Kp = 4y² / (x-y)
Solving for x from the first equation:
x + y = 1 atm
x = 1 atm - y
Substitute x = 1 - y in the Kp expression
0.85 = 4y² / ( 1 - y - y)
0.85 = 4y² / 1 -2y
0.85 - 1.7y - 4y² = 0
Solving the quadractic equation:
where a = -4, b = -1.7 c = 0.85
y = (-b +- √(b² - 4ac)) / (2a)
y =(1.7 +-√((-1.7)² - 4 (-4) × 0.85) / 2 × (-4)
y = 0.295 or y = -0.720
We take positive value of y only.
Since partial pressure of NO₂ in equilibrium is 2y
Partial pressure of NO₂ = 0.295 × 2
Partial pressure of NO₂ = 0.590 atm
Therefore, the partial pressure of at equilibrium is 0.590 atm.
Learn more about about equilibrium partial pressure at: https://brainly.com/question/7183826
How many moles are there in 100.0 grams of KMnO4
Answer:
the answer rounded to the nearest hundredth is 0.63
Explanation:
Is caffeine additive?
Answer:
yes
Explanation:
yes
Draw three different Lewis structures that could be possible for ZX2, assuming that Z is the central atom and that X is not hydrogen. Both Z and X obey the octet rule. Give molecular shapes and bond angles for each structure drawn. In each case, use valence shell electron pair repulsion theory to explain why the molecular shape is possible.
Answer:
See images attached and explanation
Explanation:
I have drawn three possible structures of ZX2. We have to remember that the shapes of molecules could be predicted on the basis of the Valence shell electron pair repulsion theory.
The number of electrons on the valence shell of the central atom determines the shape of the molecule. We have also been told that X is not hydrogen.
If the two X atoms are arranged at a bond angle of 180 degrees, we could have either structure I or II. We will have these structures if the Z atom is sp2 hybridized.
Similarly, if the Z atom is sp3 hybridized, we may have structure III in which the molecule is bent with a bond angle less than 109 degrees. This may result from the presence of a lone pair on Z.
Note that all these structures obey the octet rule.
50 + 50 - 25 x 0 + 5 + 5 =
A and B react according to the scheme 2A + B C. The reaction is highly exergonic, that is, it goes to completion when A and B are allowed to react. In order to achieve the exact stoichiometry, your intention is to mix in a kettle 2.000 tons of A and 1.000 ton of B. A balance, the maximum capacity of which is 0.500 tons with 1% precision was used to weigh A and B. Assume that the molar masses of all chemical species are equal. What is the maximum possible amount of unreacted reactants?
Answer:
0.03 tons
Explanation:
From the given information, for every 0.500 tons of A and B, the maximum amount on weighing them will be:
1% of 0.5 = 0.005
Thus, for 2 tons of A; we have:
0.005 × 4 = 0.02
and, for 1 ton of B; we have:
0.005 × 2 = 0.01
However, after taking the precision into account;
The number of tons of A that reacted is = (2 - 0.002) = 1.98 tons of A
The number of tons of B that reacted is = ( 1 - 0.01) = 0.99 tons of B
So, 1.98 tons of A reacted with 0.99 tons of B to form 0.99 tons of C.
∴
For unreacted reactants, The maximum possible amount is (0.02 + 0.01) tons = 0.03 tons
A chemist adds 0.60L of a 0.20/molL sodium thiosulfate Na2S2O3 solution to a reaction flask. Calculate the millimoles of sodium thiosulfate the chemist has added to the flask. Round your answer to 2 significant digits. (in mmol)
Answer:
1.2×10² mmole of Na₂S₂O₃
Explanation:
From the question given above, the following data were obtained:
Volume = 0.6 L
Molarity = 0.2 mol/L
Mole of Na₂S₂O₃ =?
Molarity is simply defined as the mole of solute per unit litre of water. Mathematically, it is expressed as:
Molarity = mole /Volume
With the above formula, we can obtain the number of mole of Na₂S₂O₃ in the solution as illustrated below:
Volume = 0.6 L
Molarity = 0.2 mol/L
Mole of Na₂S₂O₃ =?
Molarity = mole /Volume
0.2 = Mole of Na₂S₂O₃ / 0.6
Cross multiply
Mole of Na₂S₂O₃ = 0.2 × 0.6
Mole of Na₂S₂O₃ = 0.12 mole
Finally, we shall convert 0.12 mole to millimole (mmol). This can be obtained as follow:
1 mole = 1000 mmol
Therefore,
0.12 mole = 0.12 mole × 1000 mmol / 1 mole
0.12 mole = 120 = 1.2×10² mmole
Thus, the chemist added 1.2×10² mmole of Na₂S₂O₃
What is the empirical formula of a compound that is composed of 60.94% carbon 15.36% hydrogen and 23.70% nitrogen
Answer:
C₃H₉N
Explanation:
The empirical formula of a compound is the fundamental and basic possible formula that shows the mole ratio of the atoms of each element in a molecule of the compound.
mole ratio of carbon = 60.94/12 = 5.078
mole ratio of hydrogen = 15.36/1 = 15.36
mole ratio of nitrogen = 23.70/14 = 1.693
Now; we will divide by the smallest value
So; carbon = 5.078/1.693 = 2.99 ≅ 3.0
hydrogen = 15.36/1.693 = 9.07 ≅ 9.0
nitrogen = 1.693/1.693 = 1 ≅ 1
Thus, the empirical formula is = C₃H₉N
compare and contrast synthesis reactions and decomposition reaction
Answer:
See explanation
Explanation:
Synthesis reaction and decomposition reactions are two opposing processes.
While a synthesis reaction has to do with the formation of a substance from its constituents, decomposition deals with the breakdown of a substance into its constituents.
While decomposition requires energy and is an endothermic process, synthesis is usually an exothermic process in which energy is given off as stable products are formed.
What is believed to be one of the most common mechanisms of concussions? Will give branliest
Answer:
Typical injury mechanism: Direct impact on the head is by far the most common mechanism of concussion. It may be caused by stable objects such as the floor or objects in motion (such as baseball bats or hockey sticks).
A 0.0250L solution of HCl is neutralized by 0.0780L of an unknown Mg(OH)2 solution. Also 0.050L of this Mg(OH)2 solution is neutralized by 0.0300L of a 0.20 M H3(PO3) solution. What is the concentration of the HCl solution
Answer:
[tex]M_{HCl} = 1.12M[/tex]
Explanation:
Hello!
In this case, for the first reaction we need to focus on, the neutralization of magnesium hydroxide by phosphoric acid, we can write up the following equation:
[tex]3Mg(OH)_2+2H_3PO_4\rightarrow Mg_3(PO_4)_2+6H_2O[/tex]
Whereas the acid and base react in a 3:2 mole ratio; thus, we can write:
[tex]2M_{Mg(OH)_2}V_{Mg(OH)_2}=3M_{H_3PO_4}V_{H_3PO_4}[/tex]
Now, solving for the concentration of the magnesium hydroxide solution we get:
[tex]M_{Mg(OH)_2}=\frac{3M_{H_3PO_4}V_{H_3PO_4}}{2V_{Mg(OH)_2}} \\\\M_{Mg(OH)_2}=\frac{3*0.20M*0.0300L}{2*0.050L}=0.18M[/tex]
Now, for the reaction between hydrochloric acid and magnesium hydroxide we have:
[tex]Mg(OH)_2+2HCl\rightarrow MgCl_2+2H_2O[/tex]
[tex]2M_{Mg(OH)_2}V_{Mg(OH)_2}=M_{HCl}V_{HCl}[/tex]
Therefore, solving for the concentration of the hydrochloric acid solution we get:
[tex]M_{HCl}=\frac{2M_{Mg(OH)_2}V_{Mg(OH)_2}}{V_{HCl}} \\\\M_{HCl}=\frac{2*0.18M*0.078L}{0.025L}\\\\M_{HCl} = 1.12M[/tex]
Best regards!
chemistry
Definition in your own words. I will check if you got it from online.
Word:
Malleable
(malleability)
A particular term in an atom in which LS coupling is a good approximation splits into three levels, each having the same L and same S but different J. If the relative spacings between the levels are in the proportion 5:3, find L and S.
Answer:
Explanation:
From the information given;
Consider using Lande's Interval rule which can be expressed as:
[tex]\Delta E = E_{j+1} - E_jj \ = \alpha (j+1)[/tex]
here;
[tex]j+1[/tex] = highest level of j
and
[tex]\dfrac{\Delta E_1}{\Delta E_2} = \dfrac{(j+2)}{(j+1)}[/tex]
[tex]\dfrac{5}{3} = \dfrac{(j+2)}{(j+1)}[/tex]
[tex]5(j+1) = 3(j+2)[/tex]
[tex]5j+5 = 3j+6[/tex]
[tex]2j = 1\\ \\ j = \dfrac{1}{2}[/tex]
recall that:
[tex]j = |S-L| \ \to \ |S+L |[/tex]
So;
[tex]S-L = \dfrac{1}{2} --- (1)[/tex]; &
[tex]S+L = \dfrac{5}{2} --- (1)[/tex]
Using the elimination method, we have:
[tex]2S = \dfrac{6}{2}[/tex]
[tex]S = \dfrac{3}{2}[/tex]
Since [tex]S = \dfrac{3}{2}[/tex]; then from (1)
[tex]\dfrac{3}{2} -L = \dfrac{1}{2}[/tex]
[tex]L = \dfrac{2}{2}[/tex]
[tex]L = 1[/tex]
Liquid octane will react with gaseous oxygen to produce gaseous carbon dioxide and gaseous water . Suppose 3.43 g of octane is mixed with 3.0 g of oxygen. Calculate the maximum mass of carbon dioxide that could be produced by the chemical reaction. Be sure your answer has the correct number of significant digits.
Answer:
The maximum mass of carbon dioxide, CO₂ produced is 2.64 g
Explanation:
We'll begin by writing the balanced equation for the reaction. This is illustrated below:
2C₈H₁₈ + 25O₂ —> 16CO₂ + 18H₂O
Next, we shall determine the masses of C₈H₁₈ and O₂ that reacted and the mass of CO₂ produced from the balanced equation. This can be obtained as follow:
Molar mass of C₈H₁₈ = (8×12) + (18×1)
= 96 + 18
= 114 g/mol
Mass of C₈H₁₈ from the balanced equation = 2 × 114 = 228 g
Molar mass of O₂ = 2 × 16 = 32 g/mol
Mass of O₂ from the balanced equation = 25 × 32 = 800 g
Molar mass of CO₂ = 12 + (2×16)
= 12 + 32
= 44 g/mol
Mass of CO₂ from the balanced equation = 16 × 44 = 704 g
SUMMARY:
From the balanced equation above,
228 g of C₈H₁₈ reacted with 800 g of O₂ to produce 704 g of CO₂.
Next, we shall determine the limiting reactant. This can be obtained as follow:
From the balanced equation above,
228 g of C₈H₁₈ reacted with 800 g of O₂.
Therefore, 3.43 g of C₈H₁₈ will react with = (3.43 × 800)/228 = 12.04 of O₂
From the calculations made above, we can see that a higher mass (i.e 12.04 g) of O₂ than what was given (i.e 3 g) is needed to react completely with 3.43 g of C₈H₁₈. Therefore, O₂ is the limiting reactant and C₈H₁₈ is the excess reactant.
Finally, we shall determine the maximum mass of carbon dioxide, CO₂ produced from the reaction.
To obtain the maximum mass of carbon dioxide, CO₂ produced, the limiting reactant will be used because all of it is consumed in the reaction.
The limiting reactant is O₂ and the maximum mass of carbon dioxide, CO₂ produced can be obtained as follow:
From the balanced equation above,
800 g of O₂ reacted to produce 704 g of CO₂.
Therefore, 3 g of O₂ will react to produce = (3 × 704)/800 = 2.64 g of CO₂.
Thus, the maximum mass of carbon dioxide, CO₂ produced is 2.64 g
To isolate a single variable when re-arranging equations, move all other variables to the_____of the equation by using the____on them and remembering to perform that operation_____. Make sure the rearrangement has the target variable_____.
a. on the left side, not the right side.
b. in the numerator, not the denominator.
c. with a coefficient, not without one.
d. with a negative sign, not a positive sign.
Answer:
Other side
Opposite function
On both sides of the equation
In the numerator and not the denominator
Explanation:
To isolate a single variable when rearranging equations, move all other variables to the other side of the equation by using the opposite function on them and remembering to perform that operation on both sides of the equation. Make sure the rearrangement has the target variable in the numerator, not the denominator.
Please help quickly as possible thank you :)
Answer:
decreases a bit then stays constant
Explanation:
As the temperature of a substance increases, the average___________ energy of the particles also increases, and movement overcomes forces of ________ more easily. As temperature decreases particles move more slowly and the_________ forces between particles dominate.
Answer:
Kinetic; attraction; attraction.
Explanation:
Kinetic energy can be defined as an energy possessed by an object or body due to its motion.
Mathematically, kinetic energy is given by the formula;
[tex] K.E = \frac{1}{2}MV^{2}[/tex]
Where, K.E represents kinetic energy measured in Joules.
M represents mass measured in kilograms.
V represents velocity measured in metres per seconds square.
Conduction involves the transfer of electric charge or thermal energy due to the movement of particles. When conduction relates to electric charge, it is known as electrical conduction while when it relates to thermal energy, it is known as heat conduction.
In the process of heat conduction, thermal energy is usually transferred from fast moving particles to slow moving particles during the collision of these particles. Also, thermal energy is typically transferred between objects that has different degrees of temperature and materials (particles) that are directly in contact with each other but differ in their ability to accept or give up electrons.
Hence, as the temperature of a substance increases, the average kinetic energy of the particles also increases, and movement overcomes forces of attraction more easily. As temperature decreases particles move more slowly and the attraction-forces between particles dominate.
In conclusion, when a substance or an object is heated, a phase change starts to occur only when the average kinetic energy of its particles is great enough to overcome the force of attraction between its particles.