2.1 Thermochemistry Flashcards
What is enthalpy change?
The heat energy change measured under conditions of constant pressure
what are standard conditions?
pressure:100kPa
temperature: 298K
what is an exothermic reaction?
a reaction that transfers energy to its surroundings
what is an endothermic reaction?
a reaction that takes in energy from its surroundings
what is the sign of ΔH for endothermic and exothermic reactions?
exothermic: ΔH is -
endothermic: ΔH is +
what is the definition of the standard enthalpy change of reaction ΔrH⁰?
the enthalpy change that occurs when the quantities of reactants shown in the equation react under standard conditions, with all reactants and products in their standard states
what is the definition of the standard enthalpy change of formation ΔfH⁰?
the enthalpy change when one mole of product is formed from its constituent elements with all reactants and products in their standard states under standard conditions
enthalpy change graph (exothermic)
reactant higher than product
what is the definition of the standard enthalpy change of combustion ΔcH°?
the enthalpy change that occurs when one mole of compound is completely reacted with excess oxygen under standard conditions with all reactants and products in their standard states
enthalpy change graph (endothermic)
product higher than reactant
what is the calculation for energy transferred?
q= mcΔt
what is the equation for ΔH using q=mcΔt?
ΔH = q / n (n = mols) (q= energy)
what is the energy change using graphs calculation?
product - reactant
What is Hess’s Law?
The total enthalpy change for a reaction is independent of the route taken.
what is meant by bond enthalpy?
the energy needed to break a specific type of covalent bond, averaged out across a wide variety of different compounds
what changes can be made in a prac to make it more accurate?
polystyrene cup or add lid to prevent heat loss
measure to 0.1 for greater range
which way do arrows point for combustion?
arrows down
which way do arrows point for formation?
arrows up
definition of mean bond energy
the average energy needed to break a specific type of covalent bond average out across a variety of different gaseous species
explain why it is better to use powdered metals than a ribbon of them
powdered has a greater surface area so increases rate of reaction
where do you calculate formation?
only in compounds and in elements its always zero
Label a spirit burner practical
(enthalpy change of combustion)
- thermometer
-beaker
-clamp
-water in beaker - spirit burner
- wick in sb
- methanol inside sb
label the enthalpy change of reaction practical
-thermometer
-calorimeter
why can’t the combustion apparatus be used to determine the enthalpy change of ethene?
ethene is a gas (only works for liquids and solids)
