energetics Flashcards
define an exothermic reaction
energy has been given out of the reaction
define endothermic reaction
energy has been taken into the reaction
give one example of an exothermic reaction
neutralising an acid with an alkali
give an example of an endothermic reaction
making white anhydrous copper sulfate and water from blue copper sulfate
define enthalpy change
measuring a heat change at a constant pressure
what are the standard conditions for measuring enthalpy changes
100 kPa
298 K
why are exothermic reactions given a negative sign (-)
the products end up with less heat energy than the reactant as they lost energy when they heated up their surroundings. this means enthalpy change is negative
what are energy level diagrams used to show
enthalpy change
what is enthalpy change measured in
kJ per mole (mol-1)
define enthalpy of formation
the enthalpy change when one mole of substance is formed from its consistuent elements under standard condition, all reactants and products being in their standard states
define enthalpy of combustion
the enthalpy change when one mole of substance is completely burnt in oxygen under standard conditions, all reactants and products being in their standard states
define specific heat capacity
the amount of heat needed to raise the temperature of 1g of substance by 1K
what is the equation for calorimetry
Q = mc delta t
what is calorimetry used for
to compare the values of enthalpy change for a series of similar compounds because the errors will be similar for every experiment
how is a flame calorimeter better than a simple calorimeter
the spiral chimney is made of copper
the flame is enclosed
fuel burns in pure oxygen
what is a displacement reaction
a metal that is more reactive than another will displace the less reactive one from a compound
how do you minimise the effects of heat lost from a polystyrene cup
plotting a cooling curve
define Hess’ law
the enthalpy change for a reaction is the same independent of the route taken from reactants to products
define enthalpy change
A heat change at constant pressure
what is the difference between heat and temperature
temperature - related to the average kinetic energy of the particles in a system but is independent to the number of particles present
heat- a measure of the total energy of all of the particles present in a given amount of substance and is dependent on the number of particles
what are the 3 things you need in order to measure the enthalpy change of a reaction
- mass of the substance that is being heated up or cooled down
- temperature change
- specific heat capacity of the substance
what is the equation for enthalpy change
q = mc Δ T
why are neutralisation reactions exothermic
they give out heat
state the method that allows for heat loss in the enthalpy change practical
- Place 50 cm cubed of 1.0 mol dm-3 hydrochloric acid in a polystyrene cup and 50 cm cubed of 1.0 mol dm-3 sodium hydroxide in another
2. using a thermometer with 0.1 degrees increments take the temperature of each solution every 30 seconds for 4 minutes to confirm that both solutions remain at the same temperature as the laboratory
3. Plot a cooling graph and draw a line of best fit through these points
3. now pour the solution into the other and stir continuously and record the temperature every 30 seconds for 6 minutes
