Thermochemistry

Question 1

Important PPE for this lab includes:

Answer 1

Fully enclosed shoes, clothes covering entire torso/midriff/shoulders and entire lower body

Gloves (to be worn at all times manipulating the experimental set-up)

Lab coat

Goggles (to be worn at all times in the lab space)

Question 2

Calculate ΔH°rxn for the following reaction using the appropriate ΔH°f values, which can be found in the lab manual.

NaOH(s) + H+(aq) + Cl-(aq) –> Na+(aq) + Cl-(aq) + H2O(l)

If needed, refer to the lab manual for an example calculation of the ΔH°rxn for the decomposition of water.

Answer 2

-100.33 kJ/mol

Question 3

What is the balanced chemical reaction and the net ionic reaction for reaction 3, NaOH solid in HCl?

Answer 3

Balanced: NaOH(s) + HCl(aq) –> NaCl(aq) +H2O (l)
Net Ionic: NaOH(s) + H+(aq) –> Na+(aq) + H2O(l)

Question 4

Why do you weigh the solid NaOH by difference instead of directly weighing it on a weigh boat?

Answer 4

Sodium hydroxide is hygroscopic and will absorb water from the air, making it difficult to get an accurate mass.

Question 5

According to the Safety Data Sheet (SDS) for hydrochloric acid (HCl) the following statements are listed as hazard statements?

Answer 5

May be corrosive to metals.

May cause respiratory irritation.

Causes severe skin burns and eye damage.

Question 6

In an exothermic reaction, will the enthalpy change be positive or negative? Why?

Answer 6

Enthalpy change will be negative; the energy of the starting material is higher than the energy of the products.

Question 7

Enthalpy change ( ΔH ) is referred to as a “path function” because it is dependent on the specific mechanism of reaction, or pathway.

Answer 7

False

Question 8

Hess’s Law states that if a reaction can be written as the sum of two or more other reactions, the ΔH of the ΔH for the overall process must be the sum values of the constituent reactions.

Answer 8

True

Question 9

Learning objectives of the Thermochemistry experiment include:

Answer 9

Using calorimetry to relate measured temperature changes in chemical reactions to the reactions’ thermochemical properties.

Illustrating the concept of a state function for heats of reaction.

Demonstrating concepts, terms, and calculations of thermochemistry.