Energetics
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what is heat/ thermal energy
• a form of energy that is transferred from a warmer body to a cooler body • TOTAL kinetic energy • heat is a measure of the total energy in a given amount of substance; DEPENDS ON THE SUBSTANCE PRESENT
what is temperature
• temperature is a measure of the ‘hotness’ of a substance. It represents the AVERAGE kinetic energy of the substance, but is independent of the amount of substance present
what is an endothermic reaction
reaction which absorbs energy (bond breaking)
what is an exothermic reaction
reactions which release heat (bond making)
what is enthalpy
the heat content of a system; measured in changes
what does temperature change depend on
• mass • heat added • nature of substance
what is specific heat capacity
how much energy is required to raise the temperature of 1 g of a substance
what is calorimetry
• how enthalpy change in measured
heat equation
q= m x c x dt (Mass x specific heat capacity x temperature change)
what is thermochemistry
the study of heat changes that occur during a chemical reaction
what is hess law
it states that the enthalpy change for a reaction depends only on the difference between the enthalpy of the products and the enthalpy of the reactions -regardles of a route of a chemical reaction, the enthalpy change will always be the same
what is hess law a statement of
the law of conversation of energy
what is the standard enthalpy change of neutralization
the enthalpy change when a STRONG ACID and BASE are reacted together to form ONE MOLE OF WATER under STANDARD conditions (with everything in their standard states)
standard enthalpy change of combustion
the enthalpy change when ONE MOLE of a compound is burned in excess OXYGEN under standard conditions
standard enthalpy change of formation
enthalpy change when ONE MOLE of the compound is formed in their standard state
standard conditions
100 kPa, 298K, solutes with a concentration of 1.00 moldm-3 with the element in its standard form
standard state
the most normal, pure and stable state of a substance measured at a pressure of 100 kPa e.g. carbon: solid graphite, Carbon dioxide= gas
what is bond enthalpy
the energy required to break 1 mol of bonds in gaseous covalent molecules under standard conditions -energy needed to break a bond/energy released when a new bond is formed
bond length
as bond length decreases, bond strength increases
bond strength
the more bonds, and the shorter the bond length, the stronger
bond polarity
• can be described as the difference in the electronegativity of the bonded atoms
energy absorbed
bonds broken (endothermic)
energy released
bonds made (exothermic)
in exothermic reactions, product bond are stronger than…
reactant bonds