2.1 Thermochemistry Flashcards
What is an exothermic reaction?
A reaction that releases energy to the surroundings, there is a temperature rise and the enthalpy change is negative (ex = negative). Also the heat of products will be less than heat of reactants.
What is an endothermic reaction?
A reaction that takes in energy to the surroundings, there is a temperature drop and the enthalpy change is positive. Also the heat of products will be more than heat of reactants.
what do the terms enthalpy and enthalpy change mean?
Enthalpy is the heat content of a system and enthalpy change is the heat ADDED to a system. (this explains why if heat leaves a system the value is negative like in an exothermic reaction)
How is enthalpy change measured?
products - reactants
Draw the enthalpy profile diagram for an exothermic reaction:
Draw the enthalpy profile diagram for an endothermic reaction:
What is the principle of conservation of energy?
This principle states that energy cannot be created or destroyed only changed from one form to another.
What are the conditions for standard enthalpy change?
- All substances in their standard states
- A temperature of 298K (25 degrees)
- A pressure of 1 atm
What does standard enthalpy change of formation mean?
This is the enthalpy change when one mole of a substance is formed from its constituent elements in their standard states under standard conditions. (the ‘one mole’ is about the product)
What does enthalpy change of combustion mean?
This is the enthalpy change when one mole of a substance is completely combusted in oxygen under standard conditions. (the one mole is about the substance being combusted not the product)
What does enthalpy change of reaction mean?
This is the enthalpy change in a reaction between the number of moles of reactants shown in the equation for the reaction.
what is the calculation for enthalpy change of reaction?
sum of products - sum of reactants
What is Hess’s law?
the total enthalpy change for a reaction is independent of the route taken from the reactants to the products.
what is the difference in enthalpy cycle of combustion and reaction?
in combustion the arrows goes from the reactants to the common combustion products.
in reaction cycle the arrows goes from the common elements to the reactants and the products.
What does bond enthalpy mean?
the enthalpy required to break a a covalent X—Y bond into X and Y atoms.
what is the bond enthalpy equation?
enthalpy change of reaction = total energy needed to break bonds - total energy released in forming bonds
what can be used to accurately measure the heat transferred by a system?
calorimeter with a thermometer inside and match is to the specific heat capacity if known.
What does specific heat capacity mean?
the heat required to raise the temperature of 1g of a substance by 1K.
what is the equation for temperature change and the amount of heat transferred?
q=mc^T
q=amount of heat transfereed
^T=temp change
m=mass of the solution
c=specific heat capacity
what is the equation to calculate the enthalpy change of a reaction per mole?
^H=-q/n
