Answer:
In 5 US liquid gallons, there are 80 cups.
Explanation:
To get from gallons to cups, just multiply the amount of gallons you have by 16.
Why will the conjugate base of a weak acid affect pH? Select the correct answer below: it will react with hydroxide
Answer:
It will react with water
Explanation:
I know this is an older question, but I just wanted to provide the correct answer.
Since we are dealing with a weak base, and the acid is somewhat stronger, it will react with the water molecules to produce hydronium, which will affect the pH of the solution.
The conjugate base of a weak acid affect pH because it will react with hydronium ion.
A weak acid is an acid that does not dissociate completely in water. On the other hand, a strong acid achieves almost 100% dissociation in water.
Acids dissociate in water to yield the hydronium ion and a conjugate base. For instance, the weak acid, acetic acid is dissociated as follows;
CH3COOH(aq) + H2O(l) ⇄ CH3COO-(aq) + H3O+(aq)
We can see that the conjugate base( CH3COO-) could react with the hydronium ions thereby moving the equilibrium position to the left hand side and affecting the pH by decreasing the hydronium ion concentration.
Learn more: https://brainly.com/question/8592296
Missing parts;
Why will the conjugate base of a weak acid affect pH? Select the correct answer below: O it will react with hydroxide O it will react with water O it will react with hydronium O none of the above
Write chemical equations for the reactions that occur when solutions of the following substances are mixed:
c. OH- and H₂PO₄-
d. C₅H₅N pyridine, a base) and HC₂H₃O₂ (acetic acid)
#c
[tex]\\ \rm\hookrightarrow H_2PO_4^-+OH-\longrightarrow HPO_4^{2-}+H_2O[/tex]
H_2PO_4 is a base according to bronsted Lowry theory.So it loses a H+ and OH- takes that to form water#2
[tex]\\ \rm\hookrightarrow C_5H_5N+C_2H_4O_2\longrightarrow C_6H_6N^++C_2H_3O_2^-[/tex]
Pyridine is a bronsted base .So it forms pyridine cation by taking one H^+ from acetic acidA 6.0-L vessel was found to contain 1.0 mol BrCl 3 , 2.0 mol Br 2 and 6.0 mol Cl 2 at equilibrium. What is the equilibrium constant, K c , for this equilibrium mixture for the reaction 2BrCl 3 (g) Br 2 (g) 3Cl 2 (g)
Answer:
Writing a balanced Equation for the reaction
Br₂ + 3Cl₂ ==> 2BrCl₃
Kc = [BrCl₃]² / [Br₂][Cl₂]³
Each Concentration (n) = moles/volume of container.
(nBrCl₃)= 1/6 = 0.167moldm-³
(nBr₂) = 2/6 = 0.333moldm-³
(nCl₂) = 6/6 = 1moldm-³
Kc = (0.167)² / (0.333)(1)³
Kc = 0.0838.
Which is an intensive property of a substance?
Answer:
length
Explanation:
edge 2020
hope this helps!
Answer:
A.) Density
Explanation:
Correct on edge.
proteins contain
a. oxygen
b. nitrogen
c. hydrogen
Answer:
All of the above
Explanation:
Proteins contain a long chain of amino acids which are a chain of oxygen, nitrogen, carbon, hydrogen or sulfur.
HOPE THIS HELPED
For a sample of stomach acid that is 2.02×10−2 M in HCl, how many moles of HCl are in 14.6 mL of the stomach acid?
Answer:
0.0002949 moles
Explanation:
Concentration = 2.02×10−2 M
Volume = 14.6 mL = 0.0146 L (Upon converting to litres)
Number of moles = ?
These variables are related by the fllowing equation;
Concentration = Number of moles / Volume
Number of moles = Concentration * Volume
Number of moles = 2.02×10−2 * 0.0146 = 0.0002949 moles
Classify the following oxides as acidic, basic, amphoteric, or neutral:
(a) Select the acidic oxides:
A. CO₂
B. N₂O₅
C. Al₂O₃
D. NO
E. SO₃
(b) Select the basic oxides:
A. CaO
B. CO
C. SO₃
D. K₂O
E. BaO
(c ) Select the amphoteric oxides:
A. K₂O
B. Al₂O₃
C. CaO
D. CO₂
E. SnO₂
d) Select the neutral oxides:
A. CO
B. NO
C. SNO₂
D. N₂O₅
E. BaO
Answer:
(a).
» E. SO₃, sulphur trioxide.
(b).
» A. CaO, Calcium oxide.
» D. K₂O, potassium oxide.
» E. BaO, barium oxide.
(c).
» B. Al₂O₃, Aluminium oxide.
» E. SnO₂, tin (IV) oxide.
(d).
» A. CO, carbon monoxide.
» B. NO, nitrogen monoxide.
Explanation:
[tex]{ \underline{ \sf{ \blue{christ \:† \: alone }}}}[/tex]
How many moles of oxygen are in 49.2 grams of carbon dioxide?
Answer:
Number of mole in Oxygen = 2.24 mol
Explanation:
Given:
Amount of carbon dioxide (CO₂) = 49.2 gram
Find:
Number of moles in Oxygen
Computation:
Molecular weight of CO₂ = 44 gram (Approx)
Number of mole in CO₂ = 49.2 / 44
Number of mole in CO₂ = 1.11818182 mol
CO₂ has 2 mole of Oxygen,
So,
Number of mole in Oxygen = 2 × 1.11818182
Number of mole in Oxygen = 2.23636364
Number of mole in Oxygen = 2.24 mol
If you had a cup full of methanol and a pool full of methanol, would the mass change?
Answer:
the mass does not change
Explanation:
Based on relative bond strengths, classify these reactions as endothermic (energy absorbed) or exothermic (energy released).
Strongest Bond
A-B
A-A
B-B
C-C
B-C
A-C
1. A2 + C2 rightarrow 2AC
2. B2 + C2 rightarrow 2BC
3. A + BC rightarrow AB + C
4. A2 + B2 rightaarrow 2AB
5. AB + C rightarrow AC + B
a. endothermic
b. exothermic
Answer:
1. Exothermic 2. Exothermic 3. Endothermic 4. Endothermic 5. Exothermic.
Explanation:
1. An A-A and a C-C bond results in 2 A-C bonds which are lower than the A-A and C-C bonds so this reaction is exothermic.
2. A B-B bond and a C-C bond results in 2 B-C bonds which are lower than the first 2 bonds so this reaction is also exothermic.
3. There is no bond for single A, a single B-C bond results in a A-B bond and a C molecule. A-B bond is stronger than the B-C bond so the reaction absorbed energy along the way. This shows that it is endothermic.
4. An A-A bond and a B-B bond results in 2 A-B bonds which are stronger than the first two bonds so this reaction is also endothermic.
5. An A-B bond and a C molecule result in an A-C bond and a B molecule. A-C bond is weaker than the A-B bond so there is energy released. This reaction is exothermic.
I hope this answer helps.
Methyl iodide reacts irreversibly with azide ion with rate = k[CH3I][N3–]. CH3I(aq) + N3–(aq) → CH3N3(aq) + I–(aq) The reaction is carried out with an initial concentration of CH3I of 0.01 M. Which statement about the reaction is correct?
Answer:
(D) The reaction cannot take place in a single elementary step
Explanation:
Statements are:
(A) The time it takes for [CH3I] to decrease to 0.005 M is independent of [N3-], as long as [N3] >> [CH3I].
B) If the initial concentrations of azide and CH3I are equal, then it takes half as long for [CH3I] to decrease to 0.005 M as it does for it to decrease from 0.005 M to 0.0025 M.
(C) The reaction rate is significantly smaller if excess I- is added to the solution.
(D) The reaction cannot take place in a single elementary step.
The rate of the reaction is:
rate = k[CH3I][N3–].
That means rate depends of concentration of CH₃I as much as N₃⁻ concentration
(A) The time it takes for [CH3I] to decrease to 0.005 M is independent of [N3-], as long as [N3] >> [CH3I]. FALSE. The reaction rate depends of N₃⁻ as much as CH₃I
B) If the initial concentrations of azide and CH3I are equal, then it takes half as long for [CH3I] to decrease to 0.005 M as it does for it to decrease from 0.005 M to 0.0025 M. FALSE. Reaction is second-order. Half-life is 1/K[A]₀. If initial concentration is 0.1M, to a concentration of 0.005M it takes:
1/K*0.1. If initial concentration is 0.005M it takes 1/K*0.005. That means it takes half to decrease from 0.005M to 0.0025 as it does for it to decrease from 0.01M to 0.005M.
(C) The reaction rate is significantly smaller if excess I- is added to the solution. FALSE. Reaction rate is independent of I⁻
(D) The reaction cannot take place in a single elementary step. TRUE. As this reaction is a single-replacement reaction implies the formation of 1 C-N bond. But also the rupture of the C-I bond is impossible to explain this kind of reaction in a single elementary step.
When 2 moles of NH3(g) react with N2O(g) to form N2(g) and H2O(g) according to the following equation, 880 kJ of energy are evolved. 2NH3(g) 3N2O(g)4N2(g) 3H2O(g) Is this reaction endothermic or exothermic
Answer:
Explanation:
This is a bit of a trick question.
Usually an exothermic reaction is written as
A + B - heat = C + D
The meaning of this equation is that when the bonds of the reactants break, heat has to be given away to the environment. On the left, exothermic means that heat has to be given.
The wording on this question means that heat is a product
A + B = C + D + heat.
In other words heat is given up to the environment. So this reaction is exothermic.
A man weighs 185 lb. What is his mass in grams?
Please show work.
Thank you
Answer:
83914.52 grams
Explanation:
Given that,
Weight of a man is 185 lb
We need to find his weight in grams
For this, we must know the relation between lb and grams.
We know that,
1 lb = 453.592 grams
To find the mass of man in grams, the step is :
185 lb = (453.592 × 185) grams
= 83914.52 grams
So, the mass of a man is 83914.52 grams.
How are animals used in vaccine development?
Answer:
Animals whose certain organs closely match those of humans or have similar genetic makeup are used in vaccine tests because the results can closely resemble those same results on humans.
Explanation:
Answer:
they use them to test the effectiveness of the vaccine.
Explanation:
What is the pH of 10.0 mL solution of 0.75 M acetate after adding 5.0 mL of 0.10 M HCl (assume a Ka of acetic acid of 1.78x10-5)
Answer:
5.90
Explanation:
Initial moles of CH3COO- = 10.0/1000 x 0.75 = 0.0075 mol
Moles of HCl added = 5.0/1000 x 0.10 = 0.0005 mol
CH3COO- + HCl => CH3COOH + Cl-
Moles of CH3COO- left = 0.0075 - 0.0005 = 0.007 mol
Moles of CH3COOH formed = moles of HCl added = 0.0005 mol
pH = pKa + log([CH3COO-]/[CH3COOH])
= -log Ka + log(moles of CH3COO-/moles of CH3COOH)
= -log(1.78 x 10^(-5)) + log(0.007/0.0005)
= 5.90
Answer:
The correct answer is 5.895.
Explanation:
The reaction will be,
CHCOO⁻ + H+ ⇔ CH₃COOH
Both the HCl and the acetate are having one n factor.
The millimoles of CH₃COO⁻ is,
= Volume in ml × molarity = 10 × 0.75 = 7.5
The millimoles of HCl = Volume in ml × molarity = 5 × 0.1 = 0.5
Therefore, 0.5 will be the millimoles of CH₃COOH formed, now the millimoles of the CH₃COO⁻ left will be, 7.5-0.5 = 7.0
The volume of the solution is, 10+5 = 15 ml
The molarity of CH₃COO⁻ is, millimoles / volume in ml = 7/15
The molarity of CH₃COOH is 0.5/15
pH = pKa + log[CH₃COO⁻]/[CH₃COOH]
= 4.74957 + 1.146
= 5.895
Consider the following reaction at 298.15 K: Co(s)+Fe2+(aq,1.47 M)⟶Co2+(aq,0.33 M)+Fe(s) If the standard reduction potential for cobalt(II) is −0.28 V and the standard reduction potential for iron(II) is −0.447 V, what is the cell potential in volts for this cell? Report your answer with two significant figures.
Answer:
The correct answer is 0.186 V
Explanation:
The two hemirreactions are:
Reduction: Fe²⁺ + 2 e- → Fe(s)
Oxidation : Co(s) → Co²⁺ + 2 e-
Thus, we calculate the standard cell potential (Eº) from the difference between the reduction potentials of cobalt and iron, respectively, as follows:
Eº = Eº(Fe²⁺/Fe(s)) - Eº(Co²⁺/Co(s)) = -0.28 V - (-0.447 V) = 0.167 V
Then, we use the Nernst equation to calculate the cell potential (E) at 298.15 K:
E= Eº - (0.0592 V/n) x log Q
Where:
n: number of electrons that are transferred in the reaction. In this case, n= 2.
Q: ratio between the concentrations of products over reactants, calculated as follows:
[tex]Q = \frac{ [Co^{2+} ]}{[Fe^{2+} ]} = \frac{0.33 M}{1.47 M} = 0.2244[/tex]
Finally, we introduce Eº= 0.167 V, n= 2, Q=0.2244, to obtain E:
E= 0.167 V - (0.0592 V/2) x log (0.2244) = 0.186 V
Because of movements at the Mid-Atlantic Ridge, the Atlantic Ocean widens by about 2.5 centimeters each year. Explain which type of plate boundary causes this motion.
Answer:
A divergent plate boundary
Explanation:
At a divergent boundary, the plates pull away from each other and generate new crust.
Answer:
Because the ocean becomes larger, this is a divergent plate boundary. Divergent plates cause the ocean floor to expand, making the ocean larger.
Explanation:
PLATO ANSWER
At a given temperature the vapor pressures of benzene and toluene are 183 mm Hg and 59.2 mm Hg, respectively. Calculate the total vapor pressure over a solution of benzene and toluene with X Benzene
CHECK COMPLETE QUESTION BELOW
At a given temperature the vapor pressures of benzene and toluene are 183 mm Hg and 59.2 mm Hg, respectively. Calculate the total vapor pressure over a solution of benzene and toluene with Xbenzene = 0.580.
Answer:
The total vapor pressure is [tex]81.3 mmHg[/tex]
Explanation:
We will be making use of Dalton and Raoults equation in order to calculate the total pressure,
Which is [tex]PT= (PA × XA) +(PB ×XB)[/tex]
PT= total vapor pressure
From the question
Benene's Mole fraction = 0.580
then to get Mole fraction of toluene we will substract the one of benzene from 1. because total mole fraction is always 1.
= (1 - 0.580) = 0.420
Vapor pressure of benzene given = 183 mmHg
Vapor pressure of toluene given= 59.2 mmHg
If we substitute those value into above equation, we have
PT=(183×0.580)+(59.2×0.420)
=81.3mmHg
Therefore,, the total vapor pressure of the solution is 81.3 mmHg
The number of moles of H2O which contains 4g of oxygen?
Answer:
16G = 1 mole ; then 4G = how many moles? 4/16 = 0.25 mole; That means 4 grams of oxygen is 0.25 moles.
Explanation:
A mole of water molecules contains 2 moles of hydrogen atoms and 1 mole of oxygen atoms.
Consider the following reaction at 298K.
I2 (s) + Pb (s) = 2 I- (aq) + Pb2+ (aq)
Which of the following statements are correct?
Choose all that apply.
ΔGo > 0
The reaction is product-favored.
K < 1
Eocell > 0
n = 2 mol electrons
B-
Answer:
Eªcell > 0; n = 2
Explanation:
The reaction:
I2 (s) + Pb (s) → 2 I- (aq) + Pb2+ (aq)
Is product favored.
A reaction that is product favored has ΔG < 0 (Spontaneous)
K > 1 (Because concentration of products is >>>> concentration reactants).
Eªcell > 0 Because reaction is spontaneous.
And n = 2 electrons because Pb(s) is oxidizing to Pb2+ and I₂ is reducing to I⁻ (2 electrons). Statements that are true are:
Eªcell > 0; n = 2Explain your reasoning. Match each explanation to the appropriate blanks in the sentences on the right.
1. the atomic radius decreases
2. the number of gas molecules decreases
3. molar mass and structure complexity decreases
4. structure complexity decreases
5. molar mass decreases
6. each phase (gas, liquid, solid) becomes more ordered
A (I_2(g), Br_2 (g), Cl_2 (g), F_2 (B): The ranking can best be explained by the trend entropy decreases as______.
B (H_2O_2 (g), H_2S(g), H_2O(g): The ranking can best be explained by the decreases a trend entropy decreases as_______.
C. (C(s, amorphous), C(s, graphite), C(s, diamond): The ranking can best be explained by the trend entropy decreases as_______.
Answer:
A (I_2(g), Br_2 (g), Cl_2 (g), F_2 (B): The ranking can best be explained by the trend entropy decreases as 5. molar mass decreases.
B (H_2O_2 (g), H_2S(g), H_2O(g): The ranking can best be explained by the decreases a trend entropy decreases as 3. molar mass and structure complexity decreases.
C. (C(s, amorphous), C(s, graphite), C(s, diamond): The ranking can best be explained by the trend entropy decreases as 4. structure complexity decreases.
Explanation:
Hello.
In this case, we can understand a higher entropy when more disorder is present and a lower entropy when less disorder is present, thus:
A (I_2(g), Br_2 (g), Cl_2 (g), F_2 (B): The ranking can best be explained by the trend entropy decreases as 5. molar mass decreases since iodine has the greatest molar mass (254 g/mol) and fluorine the least molar mass (38 g/mol).
B (H_2O_2 (g), H_2S(g), H_2O(g): The ranking can best be explained by the decreases a trend entropy decreases as 3. molar mass and structure complexity decreases since hydrogen peroxide weights 34 g/mol as well as hydrogen sulfide but the peroxide has more bonds (more complex, higher entropy).
C. (C(s, amorphous), C(s, graphite), C(s, diamond): The ranking can best be explained by the trend entropy decreases as 4. structure complexity decreases since diamond has a well-ordered structure and amorphous carbon has a very disordered one.
Best regards.
A mixture of gases includes helium, neon, argon and krypton. The partial pressures are as follows:
Partial pressure, mm Hg
He 152
Ne 164
Ar 126
Kr 169
What is the total pressure of the mixture after removing the argon component? Report your answer rounded
to the nearest mm Hg but without units
Answer:
the answer to your question is ar 126
15.Vicinal coupling is:A)coupling between 1H nuclei attached to adjacent C atoms.B)coupling between 1H nuclei in an alkene.C)coupling between 1H nuclei attached to the same C atom.D)coupling between 1H nuclei in an alkane.
Answer:
A)coupling between 1H nuclei attached to adjacent C atoms.
Explanation:
The word ‘vicinal’ in chemistry means three bonds from the functional groups. The two functional groups are in a relationship with the atoms in adjacent position to them.
The 1H nuclei consists of two Hydrogen nucleus which acts as the functional groups. They are however attached and in a relationship with the adjacent C atoms. This makes option A the right choice.
An atom of 122In has a mass of 121.910280 amu. Calculate the binding energy in MeV per NUCLEON. Use the masses: mass of 1H atom
The given question is incomplete, the complete question is:
An atom of 122In has a mass of 121.910280 amu. Calculate the binding energy in MeV per atom. Use the masses: mass of 1H atom = 1.007825 amu mass of a neutron = 1.008665 amu 1 amu = 931.5 MeV
Answer:
The correct answer is 1029.95 MeV.
Explanation:
Based on the given information,
The mass of proton is 1.007825, the mass of neutron is 1.008665.
The atomic number of Indium is 49, therefore, the number of neutrons will be, 122-49 = 73.
Now the calculated mass will be,
= 49 * 1.007825 + 73 * 1.008665
= 49.383425 + 73.632545
= 123.01597
The mass defect is calculated by subtracting the actual mas from calculated mass,
Mass defect = Actual mass - Calculated mass
= 121.910280 - 123.01597
= -1.10569 amu
Now the binding energy will be,
Binding energy = 1.10569 * 931.5 MeV
= 1029.95 MeV
Beginning with Na, record the number of energy levels, number of protons, and atomic radius for each element in period 3.
Answer:
Sodium, magnesium, aluminium, silicon, phosphorus, sulfur, chlorine, and argon are the elements of third period.
Explanation:
There are three energy levels in sodium atom. It has 11 electrons revolving around the nucleus. the atomic radius of sodium atom is 227 ppm. Magnesium, aluminium, silicon, phosphorus, sulfur, chlorine, and argon has also three energy levels like sodium because all these elements belongs to third period. There are 12 electrons present in magnesium, 13 in aluminium, 14 in silicon, 15 in phosphorus, 16 in sulfur, 17 in chlorine, and 18 electrons in argon. The atomic radius of magnesium atom is 173 ppm. The atomic radius of aluminium atom is 143 ppm. The atomic radius of silicon atom is 111 ppm. The atomic radius of phosphorus atom is 98 ppm. The atomic radius of sulfur atom is 87 ppm. The atomic radius of chlorine atom is 79 ppm and the atomic radius of argon atom is 71 ppm.
When HCl is added to water, the [H3O+] = 0.6 M. What is the [OH-]?
What is the pH of the solution?
Answer:
pH=0.22.
[tex][OH^-]=1.66x10^{-14}M[/tex]
Explanation:
Hello,
In this case, since the pH is directly computed from the given concentration of hydronium ions:
[tex]pH=-log([H_3O^+])=-log(0.6M)=0.22[/tex]
It is widely known that the pH and POH are directly related via:
[tex]pH+pOH=14[/tex]
Therefore, the pOH is:
[tex]pOH=14-pH\\\\pOH=14-0.22=13.78[/tex]
Thus, the concentration of hydroxyl ions are computed from the pOH:
[tex]pOH=-log([OH^-]}\\\\[/tex]
[tex][OH^-]=10^{-pOH]=10^{-13.78}[/tex]
[tex][OH^-]=1.66x10^{-14}M[/tex]
Regards.
Which of the following processes release energy? a. ball rolling down a hill b. formation of copper (II) oxide from copper and oxygen c. formation of ice from liquid water d. condensation of water on a wind shield of a car
Answer:
d. condensation of water on a wind shield of a car
Explanation:
Condensation involves the conversion of moist air into liquid.
Gas has a higher energy compared to liquid. This is why Gas particles move at random motion and faster in relation to solid and liquid particles due to the high energy content.
The conversion of the gas to liquid means that there was loss or release of energy which validates the answer.
An equilibrium mixture of N2, H2, and NH3 at 700 K contains 0.036 M N2 and 0.15 M H2. At this temperature, Kc for the reaction N2(g) + 3 H2(g)<=> 2NH3(g) is 0.29.
What is the concentration of NH3?
Answer:
5.94×10¯³
Explanation:
The following data were obtained from the question:
Concentration of N2, [N2] = 0.036 M
Concentration of H2, [H2] = 0.15 M
Equilibrium constant (Kc) = 0.29 M
Concentration of NH3, [NH3] =.…?
The equation for the reaction is given below:
N2(g) + 3H2(g) <=> 2NH3(g)
Thus, we can determine the concentration of NH3 by using the equilibrium expression for the reaction.
This is illustrated below:
The equilibrium constant for a reaction is simply defined as the ratio of the concentration of the product raised to their coefficient to the concentration of the reactant raised to their coefficient.
The equilibrium constant for the above equation is given below:
Kc = [NH3]² / [N2] [H2]³
Inputting the value of Kc, [N2], and [H2] the value of [NH3]can be obtained as follow:
Kc = [NH3]² / [N2] [H2]³
0.29 = [NH3]²/ 0.036 × 0.15³
Cross multiply
[NH3]² = 0.29 × 0.036 × 0.15³
[NH3]² = 3.5235×10¯⁵
Take the square root of both side
[NH3] = √(3.5235×10¯⁵)
[NH3] = 5.94×10¯³
Therefore, the concentration of NH3, [NH3] is 5.94×10¯³ M.
Wine goes bad soon after opening because the ethanol dissolved in it reacts with oxygen gas to form water and aqueous acetic acid , the main ingredient in vinegar. Calculate the moles of oxygen needed to produce of acetic acid. Be sure your answer has a unit symbol, if necessary, and round it to significant digits.
Answer:
0.500 moles of oxygen
Explanation:
Full question says: "Calculate the moles of oxygen needed to produce 0.500 moles of acetic acid.
The reaction of ethanol (C₂H₅OH) with oxygen (O₂) is:
C₂H₅OH + O₂ → CH₃COOH + H₂O
Where 1 mole of ethanol reacts per mole of oxygen to produce 1 mole of acetic acid (CH₃COOH) and 1 mole of water
Based on the chemical equation (1 mole of oxygen produce 1 mole of acetic acid; Ratio 1:1). Thus, if you want to produce 0.500 moles of acetic acid you will need:
0.500 moles of oxygenThe enthalpy change for a chemical reaction is: a. the temperature change b. the amount of heat given off or absorbed c. related to molar volume d. none of the above
Answer:
b. the amount of heat given off or absorbed
Explanation:
Hello,
In this case, we should take into account a formal definition of enthalpy change such as an energetic change that occurs in a system when matter is transformed by a given chemical reaction from reactants to products. Thus, such energetic change is macroscopically exhibited and it is related with either a temperature increase or decrease; it means that if a reaction exhibits a temperature increase, we say that heat was given off and if the temperature exhibits a decrease, we say that heat is absorbed. For that reason, answer is b. the amount of heat given off or absorbed.
Regards.