Question

1. What are the similarity and difference between internal energy and enthalpy? 2. Can we measure the total enthalpy of a system directly? Please give your methods, a) if yes, how to measure; b) if no, what methods can be used to measure its change?

Answer 1

D sol:- Enthalpy & Enthalpy is the heat energy that is being absorbed or evolved during the progression Chemical reaction. The symbol is H. SH. The Change in enthalpy is given Enthalpy is the internal energy of System & and energy required to maintain volume of system at a given H = 0 + pv pressure. as * sum of where U- enthalpy sum of internal energy P- pressure of system V : volume of system ** The main difference between enthalpy and internal energy is that enthalpy Is the heat absorbed Or evolved during chemical reactions where as internal energy is Sum of potential and kinetic energy of system. es Scanne danh CamScanner

Pucc.ve: Differences Enthalpy Internal Energy H- U+ PV 1) DUE qtw 2) Defined 2) Defined as the relationship between system and the surrounding, total energy in a system. 2) SOL The total enthalpy, H , Of a system cannot be measured directly. The same situation exists in classical mechanics : nly a change camies physical meaning we must refer to defined reference point, to measure change in enthalpy can measure using calorimeter a by using formula, Enthalpy = mass i specific heat * temperature change Tes Scanned Lith CamScanner

Question #1:-) sol: No, we should not Open a refrigerator in our house to cool the room down. when you Because , as like any other machine, refrigerators generate heat first open the door you'll get a burst of cold air, An open fridge is like a waler pump in the middle of ocean. pointlessly moving stuff around. Ityl cool the room a little, but also heat it up a lot more. Question #22 Sol- is the SI unit of Yes, oc unit temperature: Centrigrade is used for temperature CS Scaunits CamScanner

Question #3:- Sol: : The more effective way of increasing thermal efficiency of carnot engine is to decrease lower temperature . Increase hi Because as we know that work can be sink Source produced by heat engine till, both do not acquire same temperature do by decreasing sink temperature increases maximum wonc output. To use increase the efficiency of actual heat engine following are required → Run the engine fuel-lean, that is, excess air. It is well known that fuel - lean running improves efficiency. → Higher compression ratio Run the engine at optimum conditions, meaning low friction & low pumping works Scanned with CamScanner

no Question 4 # SOL carnot theorem stales that heat engine working in cycle. between two constant temperature reservoirs can be more efficient than à reversible engine working between same reservoirs, Proof: U 1o B WA WB A Irrer) Rev Q-WA Q-WB T2 are * Suppose there a engines. EA ER operating between given source at temperature Ti & given sink at temperature T2 let En be irreversible heat engine E Es geversible We have to poore efficiency of EB is. than is more E cs! Scanned LAN CamScanner

San. Ve : Source be suppose both receive same quantity of heat o from at temperature Tu - Let WA & WB worlc output from engines and corresponding heat rejections be (Q-WA) E (Q-WB). Assume na > no flence WA WB ię WA>WB Ti o WA-WB B A- g-WB Q-WA Tz heat pump. Let us couple_both engines & Er is reversed which will act as It receives CQ-WB) from sink & WA from irreversible engine EnE pumps heats a to source at temperature. I Scanned with CamScanner

we → The net result is that heat WA-Wp is taken from sink & equal amount of world is produce → Hence assumption made that irreversible engine haring higher efficiency than erreversible is wrong, + Hence, it is concluded that reversible engine working between temperature limits is more efficient than irreversible engine there by proving carmot's theorem same CS Scanned with CamScanner