energetics Flashcards
(15 cards)
what is enthalpy change?
the heat energy change in a reaction at constant pressure, under standard conditions.
what are the standard conditions?
100kPa and 298K
what is an exothermic reaction?
gives out energy to their surroundings, enthalpy change is negative.
what is an endothermic reaction?
takes in energy from their surroundings. enthalpy change is positive.
what is bond enthalpy?
the energy needed to break a bond
what is the process of breaking and making bonds?
-reactant bonds are broken (endothermic)
-bonds are formed (exothermic)
what is the equation for enthalpy change?
enthalpy change= bonds broken-bonds formed
what is standard enthalpy change of formation?
the enthalpy change when 1 mole of a compound is formed from its elements in their standard stated under standard conditions.
what is standard enthalpy change of combustion?
the enthalpy change when 1 mole of a substance is completely burned in oxygen under standard conditions with all reactants and products in their standard states.
what is standard enthalpy change of reaction?
the enthalpy change when a reaction occurs in the molar quantities in the chemical equation under standard conditions will all reactants and products in their standard states.
describe how you would measure the enthalpy change of a reaction.
-put reactants in a container and use a thermometer (polystyrene to reduce heat loss)
-measure temperature at regular intervals
- plot graph
-draw lines of best fit extrapolated
-find temperature change
what is the equation to calculate enthalpy change of a reaction?
q=mcΔT
q- heat change, J
m- mass, g
c- specific heat capacity, 4.18JgK
ΔT- temperature change, K
what is Hess’s law?
the total enthalpy change for a reaction is independent of the route taken.
where do the arrows point in enthalpy of formation?
up
where do the arrows point in enthalpy of combustion and what are the products?
-down
-CO2 and H2O
