Hello Jiskha,

I'm hoping you are able to help me with my homework. Its on General Chemistry.

Question One
- When the solid NH4NO3 is dissolved in water at 25 C, the temperature of the solution decreases. What is true about the signs of enthalpy (H) and (S) for this process?

Question Two
- When a liquid evaporates, which is true about the signs of the enthalpy and entropy changes?

Question Three
- A temperature change causes the volume of a solution to increase. This change will cause:

a) the molarity and molality to increase
b) the molarity and molality to decrease
c) the molarity to inscrease but not change the molality
d) the molarity to decrease but not change the molality
e) neither the molarity nor molality to change

Thanks in advance for any help that is given. Will be much appreciated.

~ Katrina

I don't want to go through and duplicate what you may already know. Please indicate what you think about the answers and why and someone will critique your work. If you don't know where to start, please tell us what you don't understand about it.

I'm confused about these questions but I guess these answers could be possible. Let me know if i'm wrong and why. Will really appreciated it.

1) H is positive and S is negative ?
2) Both H & S are positive ?
3) Neither changes ?

Water definitely lose (-ve or exothermic) energy. But NH4NO3 gain this heat (+ve). So NH4NO3 solution gained heat from water and water got it from the surrounding so overall gained heat +ve

yeeeeeeeeeeeeeeee boi

Hello Katrina,

I'm here to help you with your General Chemistry questions. Let's go through each question and I'll explain how to arrive at the correct answers.

Question One:
"When the solid NH4NO3 is dissolved in water at 25°C, the temperature of the solution decreases. What is true about the signs of enthalpy (H) and entropy (S) for this process?"

To determine the signs of enthalpy (H) and entropy (S), we need to consider the fact that the temperature of the solution decreases. When a substance dissolves in water and the temperature decreases, it indicates an endothermic process where heat is absorbed from the surroundings. This is because the solution becomes cooler.

1) ΔH is positive and ΔS is negative: This would be incorrect since an endothermic process corresponds to a negative ΔH value, as heat is absorbed.

2) ΔH is negative and ΔS is positive: This is the correct choice. When a substance dissolves endothermically, the enthalpy change (ΔH) is negative, indicating the release of heat. The dissolving process increases the disorder (entropy) of the system (ΔS is positive), as the solid particles become dispersed in the liquid.

3) ΔH is negative and ΔS is negative: This would also be incorrect since the decrease in temperature indicates the absorption of heat, resulting in a positive ΔH value.

Therefore, the correct answer is that ΔH is negative and ΔS is positive.

Question Two:
"When a liquid evaporates, what is true about the signs of the enthalpy and entropy changes?"

During evaporation, a liquid turns into a gas, so we need to consider if this process is endothermic or exothermic, and how it affects entropy.

1) Both ΔH and ΔS are positive: This would be incorrect. While evaporation is an endothermic process (heat is absorbed from the surroundings), the entropy change (ΔS) is positive since the liquid molecules become more dispersed in the gas phase.

2) Both ΔH and ΔS are negative: This would also be incorrect since evaporation involves the absorption of heat, resulting in a positive ΔH value.

3) ΔH is positive and ΔS is negative: This is the correct choice. Evaporation is an endothermic process, so ΔH is positive. However, the process increases the disorder (entropy) of the system, so ΔS is positive.

So, the correct answer is that ΔH is positive and ΔS is negative.

Question Three:
"A temperature change causes the volume of a solution to increase. This change will cause:
a) the molarity and molality to increase
b) the molarity and molality to decrease
c) the molarity to increase but not change the molality
d) the molarity to decrease but not change the molality
e) neither the molarity nor molality to change"

When temperature changes, it can have an impact on the volume of a solution. Let's analyze the options:

a) Both molarity and molality increasing: This would be incorrect. Molarity is the amount of solute dissolved per unit volume of the solution. If the volume increases, keeping the same amount of solute, the concentration (molarity) would decrease. Molality, on the other hand, is the amount of solute dissolved per unit mass of the solvent, which is not affected by a change in volume.

b) Both molarity and molality decreasing: This would also be incorrect. As explained earlier, an increase in volume would lead to a decrease in molarity, but molality remains unchanged since it is independent of volume.

c) Molarity increasing but not changing molality: This would be incorrect. An increase in volume would cause a decrease in molarity.

d) Molarity decreasing but not changing molality: This would be correct. An increase in volume would result in a decrease in molarity, but molality remains constant as it depends on the mass of the solvent, not the volume.

e) Neither molarity nor molality changes: This would be incorrect. Only the molarity changes as a result of the change in volume.

Therefore, the correct answer is that a temperature change causing an increase in volume will result in the molarity decreasing but not changing the molality.

I hope this explanation clarifies the answers for you. If you have any further questions, feel free to ask!