# A calorimeter contains 20.0 mL of water at 15.0 ∘C . When 1.50 g of X (a substance with a molar mass of 76.0 g/mol ) is added, it dissolves via the reaction X(s)+H2O(l)→X(aq) and the temperature of the solution increases to 25.0 ∘C . Calculate the enthalpy change, ΔH, for this reaction per mole of X. Assume that the specific heat of the resulting solution is equal to that of water [4.18 J/(g⋅∘C)], that density of water is 1.00 g/mL, and that no heat is lost to the calorimeter itself, nor to the surroundings.

ΔH(mix'g)= 42.3Kj/mole

Explanation:

ΔH = (mcΔT)water/moles X

m = mass(g) = 20ml x 1.00g/ml = 20 g

c = 4.184 j/g⁰C

ΔT = 25°C- 15°C = 10°C

moles X = (1.5g)/(76g/mole) = 0.0197 mole X

ΔH = (20g)(4.184j/g°C)(10°C)/(0.0197 mole X) = 42,300J/mole = 42.3Kj/mole (3 sig.figs.)

## Related Questions

isotopes are atoms that contain the same number of protons but a different number of neutrons in their nuclei. based on this information, which statement about isotopes is true? a. isotopes are atoms of the same element. b. isotopes are atoms that have the same mass number. c. isotopes are atoms of different elements that have similar chemical and physical properties. d. isotopes are atoms of different elements that belong to the same family on the periodic table.

C)Chemical properties of elements are primarily determined by the electrons but not by the neutrons. Therefore, the Isotopes of the same element have similar chemical behavior.

A 5.5 g sample of a substance contains only carbon and oxygen. Carbon makes up 35% of the mass of the substance. The rest is made of oxygen. You are asked to determine the mass of oxygen in the sample. Which of the following expressions demonstrates a mathematical procedure to solve this problem using the proper order of operations?

We have been given the condition that carbon makes up 35% of the mass of the substance and the rest is made up of oxygen. With this, it can be concluded that 65% of the substance is made up of oxygen. If we let x be the mass of oxygen in the substance, the operation that would best represent the scenario is,

x = (0.65)(5.5 g)

x = 3.575 g

Which statement about atmospheric pressure is false? A) The warmer the air, the lower the atmospheric pressure.
B) Atmospheric pressure prevents water in lakes, rivers, and oceans from boiling away.
C) As air becomes thinner, its density decreases.
D) With an increase in altitude, atmospheric pressure increases as well.
E) Air actually has weight.

D) With an increase in altitude, atmospheric pressure increases as well.

Explanation:

Generally when altitude increases, the value of pressure decreases. This shows that pressure is inversely proportional to altitude. For example, the higher the altitude, the lower the pressure and vice versa. At very high altitude, the number of molecules of air are smaller than the number of moles of air at very low altitude. Thus, the higher the altitude, the lower the atmospheric pressure and the lower the altitude, the higher the atmospheric pressure. Therefore, option (D) is false.

The false statement is "With an increase in altitude, atmospheric pressure increases as well" because "With an increase in altitude, atmospheric pressure decreases."

Explanation:

Altitude is the vertical distance that exists between any given point on Earth and sea level.

The weight of the air that makes up our atmosphere puts pressure on the earth's surface. This pressure is known as atmospheric pressure. Generally, the more air there is over an area, the higher the atmospheric pressure. This means that atmospheric pressure changes with altitude: the higher the height of the Earth's surface with respect to sea level (altitude), the lower the air pressure.

So, the false statement is "With an increase in altitude, atmospheric pressure increases as well" because "With an increase in altitude, atmospheric pressure decreases."

According to the Law of Conservation of Mass, how many grams of product will be produced when 4 grams of reactants are involved in a chemical reaction? A. 2
B. 3
C. 4
D. 8

The answer is four. The law of conservation of mass basically says that whatever is but in will always have the same mass coming out. so for example if you had 10 grams of water and then you heated it up, it is still 10 grams of water.

C. 4

Explanation:

80 points!! I need a step by step simple experiment to show that light travels in straight lines until at a point were it enters a new medium.

Materials: laser pointer/ flashlight with a paper with a small slit, glass prism

step 1.) turn on the laser pointer point it up to the ceiling.

step 2.) point to prism, explain how the light refracts in the prism. and how it changes.

(I hope this helps!)

thanks loveeeeeee

Explanation:

Eli states that sodium phosphate is a mixture because it is composed of both sodium ions and phosphate ions. Which is the best analysis of Eli’s statement?

a. It is correct because each ion is a pure substance, so sodium phosphate is made up of two pure substances.
b. It is correct because the composition of sodium phosphate changes depending on the sample.
c. It is incorrect because sodium phosphate is a compound that has a single composition.
d. It is incorrect because the two types of ions in sodium phosphate cannot be seen.

Answer is: c. It is incorrect because sodium phosphate is a compound that has a single composition.

Sodium phosphate is chemical compound composed of atoms connected with chemical bonds.

Pure substance is made of only one type of atom (element) or only one type of molecule (compound), it has definite and constant composition with distinct chemical properties.

Pure substances can be separated chemically, not physically, that is difference between pure substances and mixtures.

C is the answer just took the test

How to balance
Mg + O2 > MgO

Mg + O2 > MgO. In reactant side, 2 O atoms and 1 Mg are present. In product side, 1 Mg and O atoms are present. Put 2 in product side to balance O atoms and 2 at Mg in reactant side to balance Mg atoms. Therefore the balanced equation becomes, 2Mg + O2 ----> 2MgO. Hope it helps.

7. An example of a compound is _____. a) chicken noodle soup b) powerade c) air inside a balloon d) lead pipe e) baking soda (NaHCO3)

E

Explanation:

A. Is wrong

To prepare chicken noodle soup, several things are needed to be mixed. This is what makes it a mixture

B is wrong

C is wrong

The air inside a balloon is usually helium which is an element and not a compound

D. Lead pipe is not a compound

E. Baking soda is a compound as it contains elements in different ratios

Explanation:

A compound is formed by chemical reaction of atoms of elements. A compound is actually formed by chemical combination of elements. A soul, a Powerade, air and a lead like are not compounds. In the first three items mentioned, on!y a mixture of substances are involved. There isn't any chemical combination at all. Lead pipe only consists of one kind of element. No other thing combines with it at all.

A solution contains a mixture of pentane and hexane at room temperature. The solution has a vapor pressure of 256 {\rm torr}. Pure pentane and hexane have vapor pressures of 425 {\rm torr} and 151 {\rm torr}, respectively, at room temperature.What is the mole fraction of hexane? (Assume ideal behavior.)

Answer: The mole fraction of hexane is 0.617

Explanation:

According to Raoult's law, the vapor pressure of a component at a given temperature is equal to the mole fraction of that component multiplied by the vapor pressure of that component in the pure state.

and

where, x = mole fraction  in solution

= pressure in the pure state

According to Dalton's law, the total pressure is the sum of individual pressures.

Thus mole fraction of hexane is (1-0.383) = 0.617 .