🔴🔸2.1 -thermochemistry Flashcards
(42 cards)
Define an exothermic reaction
A reaction that releases energy to the surroundings, there is a temperature rise and 🔼H is negative
Define an endothermic reaction
A reaction that takes in energy from the surroundings, there is a decrease in temperature and 🔼H is positive
What is the kinetic energy of matter?
The energy of motion at a molecular level
What is the cause potential energy of matter?
The positions of atoms relative to one another
What requires a change in potential energy?
Bond-breaking and bond-making
What is the internal energy of a system?
The sum of the kinetic energy of all of the particles in a system and their potential energy
Give 3 examples of exothermic reactions
- reacting acids with metals
- thermite reaction
- combustion
- respiration
Give 3 examples of endothermic reactions
- melting ice
- photosynthesis
- thermal decomposition of group 2 carbonates
Define enthalpy (H)
The heat content of a system at constant pressure
Define enthalpy change (🔼H)
The heat added to a system at a constant pressure
What is the standard pressure?
101KPA
Name an equation to calculate enthalpy change
Enthalpy of products - enthalpy of reactants
Which line is higher in an exothermic enthalpy profile, The products or reactants.
The reactants line is higher than the products therefore (🔼H) is negative
Which line is higher in an endothermic enthalpy profile, The products or reactants.
The products line is higher than the reactants therefore (🔼H) is positive
Give an example of an exothermic reaction
H2 (g) + 1/2O2 (g) —> H20 (g)
🔼H = -242
Define the principle of the conservation of energy
States that energy can’t be created or destroyed only changed from one form to another
Name the standard conditions
- all substances in standard states
- temperature of 298K (25 degrees)
- A pressure of 1 atm (101,000 Pa)
What Is enthalpy change of formation?
Enthalpy change when one mole of a substance is formed from its constituent elements
What is the standard enthalpy change of formation of carbon dioxide?
C(s) + O2 (g) —> CO2 (g)
What is the standard enthalpy of formation of carbon monoxide
C(s) + 1/2O2 (g) —-> CO (g)
Name the essential point to consider when looking at enthalpy change equations
That enthalpy change occurs at 1 mole therefore the molecule in the substance must remain at 1 mole and the other molecules must be balanced around this.
What is the enthalpy change of all elements in their standard state?
Why?
0 KJmol -1
Because there is no chemical change occurring
What is the standard enthalpy change of combustion
The enthalpy change when one mole of a substance is completely combusted in oxygen
What is the standard enthalpy change of combustion of Hydrogen
H2 (g) + 1/2 O2 (g) —> H2O (l)
