2022 Live Review 6 | AP Chemistry | Thermodynamics Multiple-Choice and Free-Response Questions

The video begins with an introduction to the AP Chemistry live review session focusing on thermodynamics and thermochemistry. Dr. Catchatory from Charlestown High School in Boston welcomes the viewers and outlines the topics to be covered, including identifying endothermic and exothermic processes, calculating enthalpy changes, analyzing calorimetry data, and relating thermodynamics to equilibrium. An optional handout is available for those who prefer written or electronic problems. The session starts with multiple-choice questions about the enthalpy of dissolving ionic solutes in polar solvents.

The paragraph delves into the principles of calorimetry and energy conservation. It discusses the heat change for water being equal and opposite to the heat change for the metal cooling process. The importance of taking time to read multiple-choice questions carefully is emphasized. The video then addresses questions related to the calculation of enthalpy change in reactions, the heat transfer between water and metal, and the reaction between sodium hydroxide and hydrochloric acid in a calorimeter. The calculations are done without a calculator, highlighting the need for mental math and estimation.

This section focuses on error analysis in a calorimetry experiment estimating the enthalpy change of a reaction. The student must identify the measured quantity affected by the error and whether it will be too high or too low. The analysis includes the impact of errors such as the volume of the acid solution added, heat loss due to poor insulation, and the final temperature being taken before thermal equilibrium. The video concludes that the least error would come from an incorrectly calibrated thermometer.

The discussion moves on to the concept of heat capacity and how it affects the temperature change in substances. It explores a scenario where different spoons are used to stir coffee and predicts which will result in the highest temperature at thermal equilibrium. The video also examines the change in average kinetic energy for samples of iron and aluminum heated to different temperatures, concluding that the change in average kinetic energy depends solely on temperature changes.

This part of the video explains the phenomenon of constant temperature during a phase change, such as the melting of a molecular solid. It describes how the heat absorbed is used to overcome intermolecular attractions rather than increasing the kinetic energy of the particles. The video also covers the calculation of the heat of fusion for methane and the determination of enthalpy and entropy changes for a phase change in water, emphasizing the principles of thermodynamics.

The video continues with an exploration of the heat of formation and Hess's law. It demonstrates how to calculate the standard enthalpy of formation for ammonia gas using given chemical equations and enthalpy values. The problem-solving approach involves manipulating equations and their corresponding enthalpy changes to find the target equation, showcasing the application of thermochemical principles.

The focus shifts to entropy changes, using particle diagrams to illustrate processes where entropy decreases. The video explains the concept that gases have more entropy than liquids or solids and that an increase in the number of gas particles leads to an increase in entropy. It guides viewers through multiple-choice questions to identify reactions with negative entropy changes, emphasizing the relationship between the number of moles of gas and entropy.

This segment presents a detailed calorimetry experiment involving the dissolution of urea in water. The student measures the temperature change, determines whether the process is endothermic or exothermic, calculates the heat of dissolution, and finds the molar enthalpy of solution. The video stresses the importance of showing all work, even for simple calculations, and provides a step-by-step guide through the experiment's calculations.

The video addresses error analysis in thermochemistry, discussing how heat transfer from the surroundings can affect the experimental molar enthalpy of solution. It provides a strategy for identifying measured quantities, determining their impact on calculated values, and explaining the relationships between different quantities. The video agrees with the student's claim about heat transfer affecting the magnitude of the experimental value.

The final paragraph explores the effect of temperature on reactions, specifically how the molar enthalpy of solution changes when cold urea is used instead of urea at room temperature. The video concludes that the molar enthalpy of solution would be larger in magnitude due to the greater temperature change. It summarizes key takeaways from the urea problem, emphasizing the importance of understanding temperature changes, endothermic processes, unit and sign accuracy, and systematic error analysis.

The video concludes with a discussion on glucose as a biochemical energy source. It covers the calculation of the empirical formula of glucose, the enthalpy of reaction for its combustion, and the standard free energy change for fermentation. The video also explains how to calculate the standard entropy change for a reaction and the effect of temperature on the equilibrium constant. It provides a comprehensive review of thermochemical principles and their applications.

The final part of the video provides a summary of the daily live review sessions available for AP Chemistry preparation. It lists the topics covered in each session, including graphical analysis, kinetics, equilibrium, and bonding, among others. The video encourages students to watch all sessions to prepare thoroughly for the exam.