Thermochemistry Worksheet

Thermochemistry: Equations

Kinetic Energy= 1/2mv2

Potential Energy= mgh
g= 9.8m/s2

Electrostatic Potential Energy= kQ1Q2/d
k=8.99x109 J-m/C2

Work= Force x Distance

ΔE= Efinal - Einitial

ΔE= q x w

W= -PΔV

H= E + PV

ΔH= ΔE + ΔPV

ΔH= H(products) – H(reactants)

q = (specific heat) x (grams of a substance) x (ΔT)
q= c x m x ΔT

qsoln = (specific heat of solution) x (g of solution) x (ΔT) = -qrxn

Bomb Calorimeter:
qrxn = (-Ccal) x (ΔT)

ΔH°rxn = Σ n ΔH°f (products) - Σ m ΔH°f (reactants)













Questions:

1. How much energy must be absorbed by 20.0 g of water to increase its temperature from 283.0 °C to 303.0 °C?

2. If it takes 41.72 joules to heat a piece of gold weighing 18.69 g from 10.0 °C to 27.0 °C, what is the specific heat of the gold?

3. A 0.1964 g sample of quinine (C6H4O2) is burned in a bomb calorimeter that has a heat capacity of 1.56 kJ/K. The temperature of the calorimeter increases by 3.2 K. Calculate the heat of combustion of quinine per gram and per mole.

4. The specific heat capacities of hafnium and ethanol are 0.146 J g-1 K-1 and 2.45 J g-1 K-1, respectively. A piece of hot hafnium weighing 15.6 g at a temperature of 160.0°C is dropped into 125 g of ethanol that has an initial temperature of 20.0°C. What is the final temperature that is reached, assuming no heat loss to surroundings?

5. The generation of 1430 J of heat inside a calorimeter causes the temperature to increase by 1.93°C. What is the heat capacity of the calorimeter?

6. The dissolution of a small amount of salt in the water in the calorimeter described in question 5 causes a temperature rise of 3.46°C. What amount of heat was evolved in the dissolution of the salt?

7. Hydrazine (N2H4) reacts with chlorine gas according to the following equation.

N2H4 (l) + 2 Cl2 (g) 4 HCl (g) + N2 (g) DH = - 420.0 kJ

Calculate the change in enthalpy for this reaction under each of the following conditions.

a. 25.4 g hydrazine reacts with excess chlorine
b. 1.45 mol HCl (g) is generated

8. Given the following two reactions and corresponding enthalpy changes,
compute the change in enthalpy for the following reaction.

5CO2 (g) + Si3N4 (s) 3 SiO (g) + 2 N2O (g) + 5 CO (g)

9. Using the table of DH°f values, determine the standard heat of reaction for the following process at 25°C and 1 atm.

a. The combustion of propane (C3H8) gas.