enthalpy

What is the definition of enthalpy

The heat content that is stored in a chemical system

What is the definition of enthalpy change

The difference between the enthalpy of the products and the enthalpy of the reactants

What is the definition of activation energy

The minimum energy required to start a reaction by breaking bonds

What is the definition of Standard conditions

-a pressure of 100kpa
-a stated temperature - usually 25 degrees c
-a concentration of 1 moldm-3 for reactions with aqueous solutions

What is the definition of standard state

The physical state of a substance under standard conditions of 100kpa and a stated temp

What is the definition of Standard enthalpy change of reaction

The enthalpy change that accompanies a reaction in the molar quantities expressed in a chemical equation under standard conditions with all reactants and products being in their standard states

What is the definition of Standard enthalpy change of formation

The enthalpy change that takes place when one mol of a compound is formed from its constituent elements in their standard states under standard conditions

What is the definition of Standard enthalpy change of combustion

The enthalpy chnage that takes place when one mole of a substance reacts completely with oxygen under standard conditions, all reactants and products in their standard states

What is the definition of Standard enthalpy change of neutralisation

The enthalpy change that accompanies the reaction of an acid by a base to form 1 mol of H2O under standard conditions, with all reactants and products being in their standard states

what does the conservation on energy law state

energy can neither be created or destroyed. therefore, in a reaction including an enthalpy change heat energy is transferred between the system and the surroundings

what are the 4 features of an exothermic reaction

-chemical system releases heat energy to surroundings
-an energy loss by the chemical system is balanced by the same energy gain by the surroundings
-enthaphy change value is negative
-temp of surroundings increace as they gain energy

what are the 4 features of an endothermic reaction

-chemical system takes in heat energy from the surroundings
-an energy gain by the chemical system is balanced by the same energy loss by the surroundings
-enthaphy change value is positive
-temp of surroundings decrease as they lose energy

what is the equation for calculating transferred heat energy for experimental data

q = m x c x change in temp

what is important to note when writing an equation for the standard enthaphy change of formation

-need to form 1 mol of a compound - careful of balancing numbers
-made from constituent elements

what would be the enthalpy chnage of standard enthalpy change of formation for elements be

there is no change so the enthalpy change would be 0

what is important to note when writing an equation for the standard enthaphy change of combustion

-need to have 1 mol of a substance - careful of balancing numbers

what is average bond enthalpy

-the energy required break one mol of a specified type of a bond in a gaseous molecule
-always endothermic
-bond enthalpy willl differ in different environments

what are the units of all standard enthalpy changes

kj mol -1

what does bendo-mexo indicate b

breaking bonds - endothermic
making baking bonds - exothermic

what is the equation for enthalpy change

sum of all reactant bonds - sum of all product bonds

what are the bonds for products and reactants in an exothermic reaction

-strong product bonds
-weak reactant bonds

what are the bonds for products and reactants in an endothermic reaction

-weak product bonds
-strong reactant bonds

what is the difference between an wnthapy level diagram and an enthalpy profile diagram

-enthalpy level diagram - only staight lines

• enthalpy profile diagram - bump for activation energy b\

what is on the y and x axis for enthalpy profile diagram and and enthalpy level diagram

y axis - enthalpy
x axis - progress of reaction

where do the arrows go for enthalpy profile diagram and and enthalpy level diagram

only in the direction there are going

what woudlnyou assume the uncertainty is of a piece of equipment if it was not listed

half of the value of the smallest increment on the measuring scale

formula for percentage uncertainty

(uncertainty/value found) x 100

formula for percentage uncertainty with two values

( 2 x uncertainty/value found) x 100

What are the features of the Kelvin scale of temperature

It starts at absolute zero and zero kelvin is equal to -273 degrees Celsius
-a 1k rise in temp is equal to a 1 degree celciys rise in temp so the value of temperature change is exactly the same in degrees Celsius and kelvin

What is specific heat capacity?

The amount of energy required to increase the temperature of 1kg of a substance by 1k. Good conductors have a small value whereas insulators have a large value

What is heat energy (Q) measured in