Exothermic, Endothermic & Calorimety (23/01/15)

Exothermic

• A reaction is exothermic when it releases heat into the surrounding environment
• 
• The thermal energy of the reactants are higher than the thermal energy of the products
• The reaction as well as it's surrounding will often gain heat
• Examples: Burning, Neutralization reactions
• 

Endothermic:

• A reaction is endothermic when it absorbs heat energy from its surrounding enviroment
• 
• The thermal energy of the reactants is lower than the thermal energy of the products
• The reaction as well as it's products get colder
• Examples:Electrolysis, Reaction between ethanoic acid and sodium carbonate
• 

During the lesson today we carried out a series of experiments to determine whether a reaction was exothermic or endothermic.

To do this we had to measure the temperature difference of the substance before the reaction to the substance after the reaction.

We carried out the experiments in a styrofoam cup to deuce the amount of heat energy that was lost to the surrounding environment.

We used the heat capacity of water and the temperatures we recorded to determine how much energy was lost or gained by the system.

20 January

20 January 2015
Bea

Today's class consisted more of lab work.

The aim of the lab was to find out if solutions of different oxides were acidic or alkaline.
The four oxides we tested were sulphur trioxide, ferric oxide, magnesium oxide, and carbon dioxide.

In order to make the oxides, we had to react substances with oxygen. For some of the substances a higher concentration of oxygen was needed rather than the one found naturally in the air.
After heating the substance using the bunsen burner, the substance was reacted with oxygen in a test tube. After adding water to the test tube, we had a solution of oxides.

To test if the solutions were acidic or alkaline, we added universal indicator to the solutions.
We were able to decipher the acidity of the solutions with varying degrees of success.

Generally a rule could be applied to the oxides.

Non-metals make acidic oxides
Soluble metals make alkaline oxides.

The iron used in the reaction did not make a soluble oxide and therefore it was difficult to obtain results from the experiment.

After the experimental part, we answered questions that related to the experiment including a question that related back to acid rain.

January 14th

Today in class we did an experiment about Halogens. Halogens are the non-metals in the 17th group of the period table. They consist of Fluorine, Chlorine, Bromide, Iodine, and Astatine. They are very reactive because they have 7 valence electrons, therefore to have a full octet they only need one electron. Reactiveness decreases down a group, therefore Fluorine in the most reactive element in group 17. This is because as the atoms go down a group more electrons are added to the element so the atomic radius increases. So the pull from the protons is weaker, therefore they react less.

During our experiment we were reacting Halogens with other Halogens that were bonded with Potassium. We found that the more reactive Halogens replaced the less reactive Halogens in the potassium solution.  In our experiment we tested this by reacting Iodine, Chlorine, or Bromine Potassium solution with Iodine, Chlorine or Bromine. If there was a reaction we could deduce that the stronger Halogen had replaced the weaker Halogen in the potassium solution. For example, 

2KBr (aq) + Cl2  = 2 KCl (aq) + Br2 

We can see there that the Chlorine oxides or displaced the Bromine because it was more reactive. 

January 9th 2015

Pardon (Again) for the late blog.

On the first lesson of the semester we were introduced to our latest topic known as periodicity(i.e. trends in chemical and physical properties across the periodic table).

Trends reviewed included shielding, overall charge, metals and non-metals, metallic character, electro-negativity, electron affinity, and other similar molecular properties covered last semester.

The homework given was to fill out a periodic table with the aforementioned trends, in order to review these trends.

January 12th: Periodicity

At the start of class, we reviewed some of the periodic table trends we had studied last class- shielding, effective nuclear charge, electronegativity, electron affinity, ionization energy, and atomic/ionic radius.



Then, in groups, we looked at some of these trends more closely- discussing what they mean, their pattern, and the causes for these patterns. Specifically we mentioned attraction, distance,  shielding, effective nuclear charge, and stability of the configuration. We looked at the impact, if any, of these factors pertaining to ionization energy trends, atomic/ionic size trends, and electronegativity/electron affinity trends.

The next thing we did was observe reactions of lithium and sodium in water as an example for the reactivity of alkali metals. We then talked about how alkali metals and halogens are the most reactive elements because they are both only one electron away from a full outer shell.

After that we received handouts for a series of presentations on periodicity, and worked on that for a short while until the end of the session.