Mothballs are composed primarily of the hydrocarbon naphthalene (C10H8). When 1.025 gof naphthalene is burned in a bomb calorimeter, the temperature rises from 24.25 ∘C to 32.33 ∘C. Find ΔErxn for the combustion of naphthalene. The heat capacity of the calorimeter, determined in a separate experiment, is 5.11kJ/∘C. Express the change in energy in kilojoules per mole to three significant figures.ΔErxn = kJ/mol

Explanation:

There are two energy flows in this reaction.

q₁ = heat from reaction

q₂ = heat to warm calorimeter .

Per the Law of Conservation of Energy,

q₁ + q₂ = 0

Data:

For the reaction

mass of naphthalene = 1.025 g

For the calorimeter

Ccal = 5.11 kJ·°C⁻¹; Ti = 24.25 °C; T_f = 32.33 °C

Calculations

(a) Moles of naphthalene

(b) ΔT

ΔT = T_f - Ti = 32.33 °C - 24.25 °C = 8.08 °C

(c) ΔE

ΔErxn = -5161 kJ/mol

Explanation:

Step 1: Data given

Mass of naphthalene = 1.025 grams

The temperature rises from 24.25 °C to 32.33 °C

Molar mass of napthalene = 128.17 g/mol

Step 2: Calculate moles

Moles = mass / molar mass

Moles naphthalene = 1.025 grams / 128.17 g/mol

Moles naphthalene = 0.0080 moles

Step 3: Calculate the amount of heat released

heat = (5.11 kJ/°C)(32.33 °C - 24.25 °C) = 41.3 kJ

Since there is heat released, this is negative = -41.3 kJ

Step 4: Calculate  Δ(Hrxn) per mole of naphthalene is:

H = (-41.3 kJ)/(0.0080 moles) = -5161 kJ/mol

ΔErxn = -5161 kJ/mol

in chemistry, adhesion and cohesion are attractive forces that exist between molecules. they hold the molecules together from each other. they are different in that adhesive force exists between molecules of different substance while cohesive force happens between molecules of same substance.

adhesion between water and glass causes water molecules at the edge of water and glass interface to climb up the wall in a narrow glass tube. this is called capillary action. cohesion is what gives glass its shape and causes water to form a droplet.