在接近绝对零的低温下,固体的热容迅速下降至接近零,因此恒定热容的假设不适用。<ref>{{cite web|last1=Franzen|first1=Stefan|title=Third Law|url=http://www4.ncsu.edu/~franzen/public_html/CH433/lecture/Third_Law.pdf|publisher=ncsu.edu|archiveurl = https://web.archive.org/web/20170709093839/http://www4.ncsu.edu:80/~franzen/public_html/CH433/lecture/Third_Law.pdf |archivedate = 9 July 2017}}</ref>由于熵是状态函数,因此温度和体积都发生变化的任何过程的熵变化都与分为两步的路径相同-恒定体积加热和恒定温度膨胀。对于理想气体,总熵变为<ref>{{cite web|url=http://www.grc.nasa.gov/WWW/K-12/airplane/entropy.html |title=GRC.nasa.gov |publisher=GRC.nasa.gov |date=2008-07-11 |accessdate=2012-08-17}}</ref> | 在接近绝对零的低温下,固体的热容迅速下降至接近零,因此恒定热容的假设不适用。<ref>{{cite web|last1=Franzen|first1=Stefan|title=Third Law|url=http://www4.ncsu.edu/~franzen/public_html/CH433/lecture/Third_Law.pdf|publisher=ncsu.edu|archiveurl = https://web.archive.org/web/20170709093839/http://www4.ncsu.edu:80/~franzen/public_html/CH433/lecture/Third_Law.pdf |archivedate = 9 July 2017}}</ref>由于熵是状态函数,因此温度和体积都发生变化的任何过程的熵变化都与分为两步的路径相同-恒定体积加热和恒定温度膨胀。对于理想气体,总熵变为<ref>{{cite web|url=http://www.grc.nasa.gov/WWW/K-12/airplane/entropy.html |title=GRC.nasa.gov |publisher=GRC.nasa.gov |date=2008-07-11 |accessdate=2012-08-17}}</ref> |