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Electromotive Force versus Electrical Potential Difference: Approaching (but Not Yet at) Equilibrium
Journal of Chemical Education ( IF 2.5 ) Pub Date : 2018-08-31 00:00:00 , DOI: 10.1021/acs.jchemed.8b00249 Leandro da Silva Rodrigues 1 , Jones de Andrade 2 , Luiz H. S. Gasparotto 1
Journal of Chemical Education ( IF 2.5 ) Pub Date : 2018-08-31 00:00:00 , DOI: 10.1021/acs.jchemed.8b00249 Leandro da Silva Rodrigues 1 , Jones de Andrade 2 , Luiz H. S. Gasparotto 1
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One of the most elusive concepts in electrochemistry is that of electromotive force (EMF). Often students, and even instructors, mistakenly take it as “electric potential difference” (EPD) or “voltage difference”. To clarify this issue properly, here we demonstrate an activity that was conducted with readily available and inexpensive resources. We employ the widely known Daniell Cell slightly modified to meet our need of measuring EMF and EPD. The key of the demonstration is to connect to the cell a potentiometer, which is an element that provides a controllable variable resistance. When the slider of the potentiometer is set to the maximum resistance, only negligible charge circulates, which brings the system to a partial equilibrium at which the potential annotated is exactly equivalent to the electromotive force. This is equivalent to opening the circuit of the cell. Upon turning the slider toward lower resistances, charge circulates with the electromotive force no longer measurable because the electrochemical cell is far from a reversible condition. Other aspects such as available work versus energy dissipation, maximum attainable work, and power comparisons are also discussed.
中文翻译：
电动势与电势差：接近（但尚未达到）平衡
电化学中最难以捉摸的概念之一是电动势（EMF）。通常，学生甚至是讲师都会错误地将其视为“电位差”（EPD）或“电压差”。为了正确地阐明此问题，在这里我们演示了一项使用容易获得且价格便宜的资源进行的活动。我们采用了众所周知的经过微调的丹尼尔（Daniell）电池，可以满足我们测量EMF和EPD的需要。演示的关键是将电位计连接到电池，电位计是提供可控可变电阻的元件。当电位计的滑块设置为最大电阻时，只有微不足道的电荷循环，这使系统达到部分平衡，在该平衡下，注释的电位正好等于电动势。这等效于断开单元的电路。在将滑块朝较低的电阻转动时，电荷以无法测量的电动势循环，因为电化学电池远非可逆状态。还讨论了其他方面，例如可用功与能量耗散，最大可达到功以及功率比较。
更新日期：2018-08-31
中文翻译：
电动势与电势差：接近（但尚未达到）平衡
电化学中最难以捉摸的概念之一是电动势（EMF）。通常，学生甚至是讲师都会错误地将其视为“电位差”（EPD）或“电压差”。为了正确地阐明此问题，在这里我们演示了一项使用容易获得且价格便宜的资源进行的活动。我们采用了众所周知的经过微调的丹尼尔（Daniell）电池，可以满足我们测量EMF和EPD的需要。演示的关键是将电位计连接到电池，电位计是提供可控可变电阻的元件。当电位计的滑块设置为最大电阻时，只有微不足道的电荷循环，这使系统达到部分平衡，在该平衡下，注释的电位正好等于电动势。这等效于断开单元的电路。在将滑块朝较低的电阻转动时，电荷以无法测量的电动势循环，因为电化学电池远非可逆状态。还讨论了其他方面，例如可用功与能量耗散，最大可达到功以及功率比较。
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