Adding water to some chemicals can be dangerous because large amounts of heat are liberated. Which of the following does NOT liberate heat when water is added to it?

KNO3 (the answer)
NaOH
Na
CaO
H2SO4

I guessed Na simply because it's the only one that's an element, but this is just random and irrelevant "reasoning." How do I go about figuring out it's KNO3 and not the others?

Experience told me the answer. Lacking that you might be able to find a table that will tell you. See if you text has one on heat of solution or enthalpy of solution. Here is a partial table I found on the web.

Thanks for the table! It actually is in my text, but I am taking the AP test soon, so I won't have a table like that. I can only answer the question based on the periodic table and that's it. Is there anything else I can use to at least eliminate the other choices?

To determine which of the given chemicals does NOT liberate heat when water is added, you will need to consider the properties and reactions of each substance.

1. KNO3 (Potassium nitrate): When water is added to KNO3, it undergoes an exothermic reaction, meaning that heat is liberated.

2. NaOH (Sodium hydroxide): When water is added to NaOH, it also undergoes an exothermic reaction, releasing a significant amount of heat.

3. Na (Sodium): Although sodium is an element, when sodium comes into contact with water, it vigorously reacts, producing hydrogen gas and releasing heat. So, water does liberate heat when added to sodium.

4. CaO (Calcium oxide): Calcium oxide reacts with water to form calcium hydroxide, releasing a considerable amount of heat during this exothermic reaction.

5. H2SO4 (Sulfuric acid): The dissolving of sulfuric acid in water is an exothermic process, releasing a large amount of heat.

Based on the information provided, KNO3 is the only substance that does NOT liberate heat when water is added to it.

To figure out which of the given chemicals does not liberate heat when water is added to it, you need to consider the types of reactions they can undergo with water. In this case, the chemicals can undergo a process known as hydration or dissolution with water, which may or may not produce heat.

One way to determine if heat is liberated during the reaction is to consider the enthalpy change or heat of dissolution. This value indicates whether the dissolution process is exothermic (liberates heat) or endothermic (absorbs heat).

One approach to finding this information is to consult a reliable reference such as a chemistry textbook or reputable online sources. These sources often provide data on the enthalpy change of dissolution for various chemicals.

In this case, you can check the enthalpy change (ΔH) of dissolution for each chemical. If the ΔH is positive, it means heat is absorbed (endothermic) during the process, whereas if the ΔH is negative, it means heat is liberated (exothermic). The chemical that does not liberate heat when water is added to it will have a positive or zero ΔH value.

By searching for the enthalpy change of dissolution for each chemical, you will find that KNO3 (Potassium Nitrate) has a positive value for its enthalpy change of dissolution. This suggests that it absorbs heat from the surroundings when it dissolves in water, rather than liberating heat. Therefore, KNO3 is the correct answer that does not liberate heat when water is added to it.

Remember, it is always advisable to consult reliable sources and references to verify the information and ensure accuracy in solving such questions.