Here we're going to say that PCl3, phosphorus trichloride, plus chlorine gas react together to give us phosphorus pentachloride. At 25 degrees Celsius, the enthalpy is negative 92.50 kilojoules. Which of the following statements are true? This is an endothermic reaction. Well, ΔH here is negative, so it is exothermic, not endothermic. If the temperatures increase, the ratio of our products over reactants will increase.
First of all, we're going to say products over reactants is talking about our equilibrium expression. So, we're talking about our equilibrium constant K. Next thing we're going to say is, let's determine the sign of ΔH and ΔS. We know that ΔH is negative because we're told that right from the beginning, so we're dealing with this one. And then what you're going to say, you can determine the sign of ΔS. We have 2 reactants combined to give us one product, so we're forming bonds, which means that ΔS is negative. So that means we fit in this slot, which means that as temperatures decrease we become more spontaneous. Okay. So we're spontaneous at low temperatures.
So if we're increasing the temperature, that's going to have the opposite effect. It's going to make us less spontaneous and more non-spontaneous. And realize when we're making a reaction more non-spontaneous, that means it doesn't want to happen. That means the reverse direction is favored. So that means that reactants are favored more than products. K. So remember K equals products over reactants. We're heading in the reverse direction where reactants become more favored, so your bottom part is becoming bigger and as a consequence, your top part is becoming smaller. So overall, what's happening to K? K would be decreasing, so this is not true. Here the ΔS for the reaction is negative? Yes. When multiple reactants combined give me one product? That is a decrease in entropy, so it's negative. And ΔG for the reaction has to be negative at all temperatures? No. It's only going to be negative or spontaneous at low temperatures. So the only statement here that's true would be option c.