Determine whether each process is exothermic or endothermic and indicate the sign of ΔH. a. natural gas burning on a stove b. isopropyl alcohol evaporating from skin c. water condensing from steam Indicate the sign of ΔH for the following processes.

Video transcript

Welcome back everyone. In this example, we need to identify the sign of entropy change for each process below, we have scenario A which describes the formation of morning dew on plants. We want to recall that in the process of formation dew, we have water going from gaseous form to liquid form where the gaseous form of water condenses into liquid drops on our plant, which has a much cooler surface. And through this process of condensation, we are observing the release of heat again to the plant's surface. And so we would say that therefore, this process is described as exothermic corresponding to a negative sign for the entropy change. And so our first answer is that we have a negative entropy sign for scenario A. Now moving on to scenario B which describes burning wood recognize that when we have wood burning, we have our wood which is reacting with oxygen gas. And this is going to be a combustion where we would form carbon dioxide and water and other combustion products. And in combustion, we should recall that we have the release of heat and light in the case of a fire to the environment. And since we have heat and light sorry heat and light being released into our environment. Although we do have a very small amount of endothermic process coming from energy required to vaporize any water molecules present in our wood structure. Because overall this process is a combustion and we have again, a very large release of heat, energy, heat and light energy, we would say that we have a net negative entropy change. And this is also an exothermic process. But for our answer, we are going to highlight that we have again, a net negative entropy change for burning wood. Now, moving on to example, c the formation of dry ice fog recognize that dry ice is formed out of solid carbon dioxide molecules which are going to instantly sublime directly into their gaseous form creating our dry ice fok. This process is known as sublimation where in order to go directly from the solid to gaseous phase, the intermolecular forces in our solid structure of CO2 become weakened through the addition of heat allowing them to be able to directly convert into the gaseous phase. And so because sublimation requires heat, we would have a delta symbol over our reaction arrow to signify the addition of heat, meaning our system being our reaction requires heat. And so our reactants absorb heat from the surroundings via an increase in temperature. So we can put a slash that heat is absorbed. And because of this reason, we would say that Therefore, this process is actually endothermic. And our sign for entropy change is going to actually be positive. And this would be our third answer. So all three of our answers highlighted in yellow correspond to choice a in the multiple choice to complete this example. So I hope this was helpful and let us know if you have any questions.