Chemistry (Chemical Reactions and Stoichiometry)

Question 1

What is enthalpy?

Answer 1

The total energy preseent in a substance.

Question 2

What does enthalpy include?

Answer 2

• Chemical potential energy which is the energy stored in bonds.

Question 3

What is common to all chemical reactions? (equation of enthalpy)

Answer 3

ΔΗ = Ηproducts - Hreactants

Question 4

What is an exothermic reaction? Is the change in enthalpy positive or negative? And an example?

Answer 4

One that releases energy to its surroundings. The change in enthalpy is negative as the products have less energy than the reactants, because of the released energy.

Question 5

What is an endothermic reaction? Is the change in enthalpy positive or negative? And an example?

Answer 5

One that absorbs energy from its surroundings. The change in enthalpy is positive as the products have more energy than the reactants, because of the energy drawn from the environment.

Question 6

Is the breakage of a bond endothermic or exothermic?

Answer 6

Endothermic because energy must be supplied to break the bond. Breaking a bond requires the input of energy to overcome the attraction between the bonded atoms and to break their electron interactions.

For example, breaking an ionic bond, such as in sodium chloride, requires the input of energy to separate the oppositely charged ions. The energy required to break the bond is equal to the amount of energy that was released when the bond was formed.

Question 7

Is the formation of a bond endothermic or exothermic?

Answer 7

Exothermic, because energy is released when the bond is formed. When atoms come together to form a bond, their electron clouds interact and rearrange to form a more stable configuration. This process releases energy in the form of heat or light, depending on the type of bond.

For example, in the formation of an ionic bond, such as between sodium and chlorine, the transfer of electrons from sodium to chlorine results in the release of energy, which is typically in the form of heat. This energy is released because the resulting compound, sodium chloride, is more stable than the separate sodium and chlorine atoms.

Question 8

What is Stoichiometry

Answer 8

The calculation of relative quantities of reactants and products in chemical equations.

Question 9

What is the formula to find # of particles?

Answer 9

Number of particles = (Number of moles) x (6.022x10^23)

Question 10

What are the steps taken to find the mass of a product?

Answer 10

1. Calculate the number of moles of the given mass
2. Use the mole ratio from the balanced equation to find the number of moles of the unknown product
3. Calculate the mass of the product from its number of moles (using the # of moles = # of particles / 6.022x10^23 or n = m/M)

Question 11

What are the steps taken to find the elemental composition?

Answer 11

1. Calculate the relative atomic mass of the desired element.
2. Find the total Molar Mass
3. Divide the Ar by the total Molar Mass

Question 12

What is the formula to find the molarity of a solution?

Answer 12

Molarity = moles of solute/volume of solution in litres

Question 13

How many moles of Fe+ ions and SO4(2-) ions are contained in 1.8 moles of Fe2(SO4)3?

Answer 13

Fe: 3.6 moles
SO42-: 5.4 moles