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Heat is required to make the reaction occur.
Wiki User
∙ 11y ago
Dilim
Wiki User
∙ 14y agoThis is actually trickier than it sounds, because it depends on the particular conventions you're using. I studied thermodynamics in two different classes, one chemistry and and one physics, at the same time ... and the two textbooks used different conventions for the sign of delta-H. The physics book used a positive delta-H to mean that you could get work OUT of the system (exothermic), the chemistry book used a positive delta-H to mean you had to put work INTO the system (endothermic). The best thing is to review your textbook and see which convention they use.
Wiki User
∙ 8y agoTypically, exothermic reactions have negative enthalpy, But this may not always necessarily be the case.
To prove this we say that H=U+PV and U=Q+W (H=enthalpy, U=internal energy, P=pressure, V=volume, Q=heat, W=work).
H=U+PV
Substitute for U (see above)
H=Q+W+PV
Take the differential of dH:
dH=dQ+dW+d(PV)
Plug in for dW with dW=-P(deltaV)) (this is true for a ideal gas expanding against constant external pressure)
dH=dQ-P(deltaV)+d(PV)
Take the derivative of d(PV) using the chain rule
dH=dQ-P(deltaV)+P(deltaV)+V(deltaP)
Cancel like terms
dH=dQ+V(deltaP)
At constant pressure (which is what is normally observed in almost all naturally occurring environments the pressure is constant so the V(deltaP) term is 0 (change in volume is zero) and therefore dH=dQ. So in this case, if Q is negative so is enthalpy. However, if are at constant volume conditions (example: a bomb calormiter) where the pressure can change it may be possible to have a V(deltaP) term that is greater than the negative Q (indicating the reaction is exothermic while still giving you a positive enthalpy.
Example: dQ=-1000J (Exothermic process) V=(5L) deltaP=2atm
dH=dQ+V(deltaP)
dH=-1000J+10L*atm=-1000J+1013.25J=13.25... (10Latm=1013.25J)
dH is positive while the process is exothermic. I understand these conditions are extreme and unlikely, but they are being used to illustrate a point - mathematically, and potentially IRL, it is plausible to have an exothermic process with a positive change in enthalpy.
Wiki User
∙ 13y agoyes
Wiki User
∙ 12y agonegative
Are titrations endothermic or exothermic?
In thermometric titration the reaction enthalpy is used to follow the chemical reaction. I guess it dépends on the titration reaction it can be exothermic or endothermic. ΔHr (molar heat of reaction) negative (indicating an exothermic reaction) or positive (indicating an endothermic reaction
Is polymerization endothermic or exothermic?
Exothermic, because the reaction enthalpy must be negative. With polymerization, the entropy decreases. The Gibbs energy has to be negative. Thus negative reaction enthalpy. Gibbs energy = reaction enthalpy - temperature*entropy
What kind of enthalpy change favors a spontaneous reaction?
An exothermic reaction is a chemical reaction that releases energy in the form of heat. It favors a negative enthalpy change.
In an exothermic reaction is the energy of the products higher or lower than that of the reactants?
In an exothermic reaction the energy of the products is less than that of the reactants.
What is heat of reaction and enthalpy of reaction?
Heat of reaction and enthalpy of reaction are the same thing. Enthalpy, or the heat transfer, cannot be measured, however we can measure the CHANGE of enthalpy which is shown by a value of ∆H. This measured in kilojoules per mole of reactant. (KJ/mol)This value may be positive or negative. For endothermic reactions (which absorb heat), the ∆H value is always positive. For exothermic, where heat is released, the value is negative.
What does it mean if the change in enthalpy value for a chemical reaction is positive?
Change in enthalpy value for a chemical reaction is positive is because,there loose of electron(s) in the reaction, and that will change the enthalpy of that particular element from negetive,neutral to positive.
Is vaporisation an exothermic or endothermic process?
Any reaction categories into exothermic and endothermic based upon change in enthalpy of reaction. If difference in enthalpy of product and reactant comes positive value then it is termed as endothermic and if it is negative value then exothermic reaction. Usually, vaporisation is considered as exothermic due to release in energy.
Are titrations endothermic or exothermic?
In thermometric titration the reaction enthalpy is used to follow the chemical reaction. I guess it dépends on the titration reaction it can be exothermic or endothermic. ΔHr (molar heat of reaction) negative (indicating an exothermic reaction) or positive (indicating an endothermic reaction
What is process that involves absorption of heat?
endothermic reaction a positive enthalpy.
Is polymerization endothermic or exothermic?
Exothermic, because the reaction enthalpy must be negative. With polymerization, the entropy decreases. The Gibbs energy has to be negative. Thus negative reaction enthalpy. Gibbs energy = reaction enthalpy - temperature*entropy
What kind of enthalpy change favors a spontaneous reaction?
An exothermic reaction is a chemical reaction that releases energy in the form of heat. It favors a negative enthalpy change.
What is the sign of ΔT in an endothermic reaction?
ΔH is the enthalpy of the reaction and will be positive in an endothermic reaction and negative in an exothermic reaction.ΔT designates a change in temperature. T2-T1 = ΔTOften the change in temperature will be negative for an endothermic reaction.
In an exothermic reaction is the energy of the products higher or lower than that of the reactants?
In an exothermic reaction the energy of the products is less than that of the reactants.
How do you know if an enthalpy change diagram is endothermic or exothermic?
If you plot the reaction coordinate (what I think you mean by "enthalpy change diagram"), the reaction will be exothermic if the products are lower on the graph than the reactants. If they are higher than it is endothermic. For instance, if you go to the linked Wikipedia page (link to the left of this answer), the graph shown is of an exothermic reaction.
What type of reaction is exothermic reaction?
The reaction in which energy is being released, and the overall energy change (enthalpy) is negative.
What is heat of reaction and enthalpy of reaction?
Heat of reaction and enthalpy of reaction are the same thing. Enthalpy, or the heat transfer, cannot be measured, however we can measure the CHANGE of enthalpy which is shown by a value of ∆H. This measured in kilojoules per mole of reactant. (KJ/mol)This value may be positive or negative. For endothermic reactions (which absorb heat), the ∆H value is always positive. For exothermic, where heat is released, the value is negative.
What is the sign of the enthalpy change for an endothermic reaction?
Endothermic reaction: In an endothermic reaction, the products are higher in energy than the reactants. Therefore, the change in enthalpy is positive, and heat is absorbed from the surroundings by the reaction therefore enthalpy change show positive sign in a endothermic reaction..
