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16 Cards in this Set

  • Front
  • Back

Enthalpy change

The change in energy as reactants turns into products.


This is symbolized by


delta H


'Delta'means the change in


'H' means stored heat energy.

Exothermic reactions

Energy is released by the system and goes into the surroundings.


Less energy is absorbed from the surroundings


The reactants have higher energy than the products ,thus surroundings increase in temperature


The value of delta H is negative

Endothermic reactions

Energy is absorbed from the surroundings by the system.



The products have higher energy than the reactants .



The system is warmed up


The value of delta H is positive

Three formats used to communicate enthalpy change

1.Thermochemical equation with delta H as a product



2.Thermochemical equation with delta H as a separate term



3.Potential energy diagram

Thermochemical equation

This is a balanced chemical equation with the energy on the product side .



Example: N2 + 3H2 ------> 2NH3 + 92kj


Thermochemical equation with delta H as a separate form

N2 + 3H2------> 2NH3 delta H= -92KJ

Calculating the quantity of heat

Q=mcdeltaT


1joule=1000 KJ always convert to joule


1L =1000mL



%error= (theoretical value- experimental value )÷theoretical value×100



Units for measuring heat is always KJ.


Specific heat capacities

The units of heat capacities are J/g/°C.


Heat capacity is the amount of heat needed to heat 1g of substance by 1°C



Solids have lower specific heat capacities than liquids.



Use GUESS format for solving problems.



G- given


U- unknown


E- equation


S- substitute


S- solve


Formula for conversation

n=m/M



1000mL=1L


Difference between ' bomb' calorimeter and calorimeter that already has a heat soutce

In a bomb calorimeter heat from the reaction is transferred to the metal chamber and to the water,but not beyond . Heat does not escape into the air.



Heat escapes from a calorimeter with heat source.


.






Calorimetry

Calorimetry is the process of determining the heat lost or gained by an experiment.


Calorimeter

A calorimeter is a device used to allow someone to experimentally make measurements as some endothermic or exothermic reactions occur.

HESS law

This method is used when the delta H for reactions could not be calculated using the calorimetry system.



The main equation is the target equation. Sometimes you'll have to add two or more given equations to arrive at your delta H value. Note the equations added must sum up to your target equation. Sometimes reversing an equation is possible too. When reversing an equation you have to reverse the sign of the delta H value also.

Heats of formation

This is another method used to determine the enthalpy change a reaction.



Delta H= the sum of delta H° (products)+the sum of delta H° for (reactants)

Hybrid cars

Hybrids were invented by Geoffrey Ballard.



Hybrids has both an electric and gasoline engine


The energy emitted by these cars is clean


They have regenerative breaking which allow less energy consumption



Great city mileage



Advantage is that they are expensive to maintain and to replace a damage part can be hard since they don't have much part for those type of cars on the market.

Rates of reaction

Rate means how quickly or slowly something happens.



The independent variable is time and the dependent variable is quantity. This is so because the quantity reacted is dependent on the amount of time passed.



Rate =delta(×)÷delta t. So this means concentration or amount divided by time equals rate at which reaction occurred. Square brackets must be used to enclose concentration in chemistry.



A spectrophotometre is used to measure when substances are dissolved in liquids.



A special probe is used to measure the electrical conductivity of a solution at set intervals.



There are two different rates to be considered.:


The instantaneous rate -thisbis the rate at a certain point in time. This is found by drawing a tangent to the curve at a specified time.



The Average rate- the rate for a given period of time. The time may be an entire reaction or it may be the first few seconds.


These are classified as using the slope formula.



Positive slopes means products forming (concentration increases with time. Negative means reactants.



When finding instantaneous or average rate



rate= delta (×) Rise


------------------


÷ delta (t) Run


THEN



Rate = (A)2-(A)1


---------------


T2-T1


--------------------


T2-T1