Home › WAEC WASSCE › Chemistry › Thermochemistry › In the first law expression relating internal en…
In the first law expression relating internal energy change to heat and work, when is the work term positive?
AWhen work is done on the system
BWhen work is done by the system
CWhen heat flows out of the system
DWhen the volume of the system rises
Answer & Solution
Correct answer: A. When work is done on the system
1. Internal energy changes by heat flow plus work.
2. Heat flowing in counts as positive and heat flowing out as negative.
3. Work is positive when the surroundings do work on the system.
4. Work is negative when the system does work on the surroundings, as in expansion.
5. Bending a wire back and forth does work on it, so its internal energy and temperature rise.
_Source: OpenStax Chemistry (CC BY 4.0), Ch 5 "Thermochemistry", section 5.3 Enthalpy_
Related questions
The energy needed to raise the temperature of water depends on atmospheric pressure and onThe specific heat of a substance is usually treated as constant across a chapter's temperaA flask of water heated from 21 degrees Celsius to 85 degrees Celsius has absorbed heat, sHeating 800 grams of water by one degree Celsius requires how many times the energy neededCompared with chemical reactions, the energy changes in nuclear reactions are larger by a Increasing the thermal energy of a sample raises its temperature, provided that:In a bimetallic strip thermometer, brass and steel are paired because on heating:Most metals have specific heats that are: