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No, when H and S are both negative, the reaction will only be spontaneous below a certain temperature

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Are endothermic reactions always nonspontaneous?

No, many exothermic reactions need the heat of activation to start the reaction. Paper, for instance, does not spontaneously burst into flame... you need to raise its temperature to the kindling point for it to burn.


A chemical reaction has a positive H value and a positive S value Under what conditions is the reaction spontaneous?

The spontaneity of a reaction is determined by the sign of the Gibbs free energy (ΔG). If both enthalpy (H) and entropy (S) are positive, the reaction can be spontaneous at high temperatures where the TΔS term outweighs the positive ΔH term, resulting in a negative ΔG. This means the reaction will be spontaneous at elevated temperatures.


Why do chemical reactions always involve a chemical change?

Chemical bonds always break in chemical reactions, causing changes in energy.


When is a reaction always spontaneous according to Gibbs free energy equation?

A reaction is always spontaneous when the change in Gibbs free energy (ΔG) is negative (ΔG < 0). This occurs when the system's enthalpy change (ΔH) is negative and the entropy change (ΔS) is positive, or when the temperature is sufficiently low to make the term TΔS (where T is temperature) less significant compared to ΔH. In summary, spontaneous reactions can be identified by a negative ΔG value, indicating that they can occur without external input.


When chemical reactions occur energy is always absorbed?

No, chemical reactions can be endothermic or exothermic.


Why do reactions always involve a change in energy?

Chemical bonds always break in chemical reactions, causing changes in energy.


Is the spontaneity of reactions always associated with exothermic heat release?

No, the spontaneity of reactions is not always associated with exothermic heat release. Some spontaneous reactions can be endothermic, meaning they absorb heat from their surroundings.


Do Chemical reactions involve the interplay of the electrons of the reacting chemical?

always.


What determine whether a reaction took place?

Use the following equation: delta G = delta H - T*deltaS. A reaction is spontaneous if delta G is negative. A reaction will always be spontaneous (under any temperature) only if the change in enthalpy (delta H) is negative and the change in entropy (delta S) is positive. If this is not the case, the reaction will only be spontaneous (negative delta G) for a range of temperatures (or could be always non-spontaneous)


Do chemical reactions always involve changes in energy?

no


Is spontaneous reaction exo or endo?

Reactions are described by this equation: GD = HD - TDS where D = delta for change in values. GD < 0 spontaneous HD < 0 exothermic ; HD > 0 endothermic The first equation is Gibbs free energy. When G is negative, the reaction is spontaneous. In contrast, a positive number G is non spontaneous. The interesting thing is that spontaneous reactions can be EITHER exothermic and endothermic. Lets look at this: lets assume HD has a value of 100. This means TDS would have to be bigger than 100 in order to make GD a negative number. An endothermic reaction which has a positive H can still be exothermic. Here's another way to pose your question: Is an exothermic reaction spontaneous? Always. Is an endothermic reaction spontaneous? This can be either.


Why is fluorine's oxidation number always negative?

Fluorine is the most electronegative element, meaning it has a strong tendency to gain electrons in chemical reactions. This leads to a stable octet configuration, resulting in a negative oxidation number (-1) when forming compounds.