Does an exothermic reaction have to be spontaneous?

All spontaneous processes are not exothermic, because it is the Gibbs Free energy that determines spontaneity, not the enthalpy. You will notice that this expression may be positive even with a negative enthalpy change (exothermic process) if the entropy change is negative and the temperature is high enough.

Why are endothermic reactions spontaneous?

For endothermic reactions, enthalpy usually goes up. However, a spontaneous endothermic reaction can occur when the changes in enthalpy and entropy yield a negative Gibbs free energy. An endothermic reaction can be spontaneous if entropy increases by more than the change in enthalpy.

Why are there exothermic reactions that are not spontaneous?

Re: Non-spontaneous exothermic reaction An exothermic reaction may be non-spontaneous if the reaction also leads to a decrease in entropy. Once temperature is above a certain point, this means the reaction becomes entropy-driven, causing the reaction overall to have a positive deltaGo.

What reactions are always exothermic?

All combustion reactions are exothermic reactions. During a combustion reaction, a substance burns as it combines with oxygen. When substances burn, they usually give off energy as heat and light.

What is always true of spontaneous reactions?

According to the Second Law of Thermodynamics, a reaction is spontaneous if the overall entropy, or disorder, increases. In a spontaneous reaction, just because the overall change in entropy is positive does not mean that the entropy of the systems and surroundings should always both be positive.

What is the difference between spontaneous and non-spontaneous process?

Processes have a natural tendency to occur in one direction under a given set of conditions. A spontaneous process is one that occurs naturally under certain conditions. A nonspontaneous process, on the other hand, will not take place unless it is “driven” by the continual input of energy from an external source.

Are all spontaneous processes exothermic?

Generally, all spontaneous processes are not exothermic, since the Gibbs Free energy that determines spontaneity, not the enthalpy. Any process is said to be spontaneous if the Gibbs free energy is negative.

How do you know if an endothermic reaction is spontaneous?

An endothermic reaction may be spontaneous because of an increase in entropy. Spontaneity can be indicated by the sign of Gibb’s free energy, ΔG. ΔG = ΔH – TΔS where ΔH is the enthalpy change (the thermal part) and ΔS is the change in entropy. For a reaction to be spontaneous ΔG must be negative.

Are all reactions exothermic at standard state?

No, but all reactions that are spontaneous at standard state (interpreted to mean that at standard state, equilibrium lies in the forward direction, i.e. K > 1 and $\\Delta_r G^\\circ < 0$) are either exothermic ($\\Delta_r H^\\circ < 0$) or show a positive standard entropy of reaction ($\\Delta_r S^\\circ > 0$), or both.

How do you know if a process is spontaneous?

A process is spontaneous if the Gibbs free energy is negative. An important expression for the Gibbs free energy is given by You will notice that this expression may be positive even with a negative enthalpy change (exothermic process) if the entropy change is negative and the temperature is high enough.