Enthalpy Change of Reaction & Formation - Thermochemistry & Calorimetry Practice Problems

TL;DR

Learn how to calculate enthalpy change and heat transfer in reactions using formulas and specific heat capacities.

Transcript

in this video we're going to focus on how to calculate the enthalpy change of a reaction so consider the combustion reaction of ethanol c2h5oh in the combustion reaction you have a hydrocarbon which usually reacts with o2 the products of a combustion reaction is always going to be co2 and water now go ahead and pause the video and balance the react... Read More

Key Insights

• 🙃 Balancing combustion reactions involves ensuring the same number of atoms on both sides, starting with carbon, then hydrogen, and finally oxygen.
• 👻 Hess's law allows the calculation of the enthalpy change of a reaction by adjusting and combining balanced equations and summing the enthalpies of the individual reactions.
• 💁 Enthalpy change of formation is the same as the enthalpy of a reaction where a compound is produced from its elements in their natural state.
• 😆 Heat transfer in reactions can be measured using calorimetry, which involves a calorimeter and the formula q = mcΔt.
• 💱 Phase changes involve conversions between solid, liquid, and gas states, with specific heat capacities and enthalpy changes associated with each process.

Questions & Answers

Q: How can you calculate the enthalpy change of a reaction using the heats of formation for the reactants and products?

To calculate the enthalpy change of a reaction, you can use the equation The change in enthalpy of the reaction is equal to the sum of the enthalpies of formation for the products minus the sum of the enthalpies of formation for the reactants.

Q: What is Hess's law and how can it be used to calculate the enthalpy change of a reaction?

Hess's law states that the enthalpy change of a reaction is independent of the pathway taken to reach the products and depends only on the initial and final states. To calculate the enthalpy change, you adjust and combine balanced equations in such a way that they add up to the desired reaction. Then, you sum up the enthalpies of the individual reactions to get the total enthalpy change.

Q: How can you use calorimetry to measure heat transfer in reactions?

Calorimetry involves using a calorimeter, a device that measures the heat exchange in a reaction. By knowing the specific heat capacity of the substance being heated or cooled and measuring the mass and temperature change, you can calculate the heat transfer using the formula q = mcΔt.

Q: What is the enthalpy change of formation, and how does it relate to the enthalpy of reaction?

The enthalpy change of formation is the enthalpy change in a reaction where one mole of a compound is formed from its elements in their natural state. The enthalpy change of reaction is equal to the sum of the enthalpy changes of formation for the products minus the sum of the enthalpy changes of formation for the reactants.

Summary & Key Takeaways

• The video explains how to balance a combustion reaction and calculate the enthalpy change of the reaction using the heats of formation for each substance.

• Hess's law is introduced as a method to estimate the enthalpy change for reactions by adjusting and combining balanced equations.

• Enthalpy of formation is defined as the enthalpy change of a reaction where one mole of a compound is produced from its elements in their natural state.

• Calorimetry is discussed as a way to measure heat transfer in reactions by using the equation q = mcΔt and converting between joules and kilojoules.

• Phase changes (freezing, melting, vaporization, condensation, sublimation, and deposition) are explained, along with whether they are endothermic or exothermic processes.