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Chemistry grade 10 By Kako and Oscar (Green Chemistery (Atom Economy, Less…
Chemistry grade 10 By Kako and Oscar
Green Chemistery
Atom Economy
Less Hazardous Chemical Synthesis
Waste Prevention
Designing Safer Chemical
Safer Solvents&Auxiliaries
Design for energy Efficiency
Use of renweable Feedstocks
Reduce Derivatives
Catalysis
Design for Degradiation
Real-time pollution Prevention
Safer chemistry for accident Prevention
Heat of reaction
Endothermic reaction
Photosynthesis
Melting ice
Sublimation of carbon dioxide (dry ice)
Exothermic reaction
Ice cubes (when water freezes)
Lighting of Match
Burning Candles
Exothermic reaction is when energy is being released from the process through light or heat
Endothermic reaction is when heat or energy is being absorbed from its surrounding
Chemical equations
Any reaction can be represented by a chemical equation with the following form:
reactants → products
the atoms are rearranged and form new bonds to create the products
Balancing chemical equations
We do this by placing whole numbers in front of chemical formulas as needed. These are known as coefficients and they tell you the relative amounts of the chemicals involved in the reaction
Balance the equation by adding coefficients.
Na + H2O = NaOH + H2
2Na + 2H2O = 2NaOH + H2
Haber reaction (ammonia)
The Haber process is an example of a composition reaction, also known as a combination or synthesis reaction. In this type of reaction two or more reactants join together to form a single product. The general form is given by the following equation:
A + B → AB
nitrogen gas + hydrogen gas → ammonia gas
N2 (g) + 3H2 (g) → 2NH3 (g)
One of the explosives produced from ammonia is nitroglycerin, the key ingredient of dynamite. This highly dangerous liquid breaks down to produce a rapidly expanding mixture of gases:
nitroglycerin liquid → nitrogen gas + carbon dioxide gas + water vapour + oxygen gas
4C3H5N3O9 (l) → 6N2 (g) + 12CO2 (g) + 10H2O (g) + O2 (g)
Rusting
Corrosion
Metal objects corrode (destroy or damage slowly by chemical action) when it's exposed to the open air and the bad weather
If the metal is iron, we can call this change rusting
the weaker, flaky brown compound that is formed is "rust"
Salt solution acts as an electrolyte (any substance containing free ions that aloows the substance to conduct electricity)
Allowing ions to lose electrons more easily, and speeds up the rusting process
Chemical Equation of "Rust"
4Fe(s) + 3O2(g) + xH2O(l) --> 2Fe2O3xH2O
the x is a variable for amount of water
Word Equation of "Rust"
iron + oxygen + water --> hydrated iron (III) oxide (RUST)
Composition/Decomposition
To produce ammonia by the Haber process high temperatures are used to speed up the reaction. The problem with this is that heat causes some of the ammonia to break down into nitrogen and hydrogen again. One way of maximizing the amount of ammonia produced is to continually extract it from the reaction chamber and cool it to liquid form.
The breakdown of ammonia to nitrogen and hydrogen is an example of a decomposition reaction. This is when a single reactant breaks down into two or more products:
AB → A + B
Precipitation reactions
Precipitation reactions generate solid products that settle out of solution. These are known as precipitates. They are often brightly coloured compounds and can be used as pigments, like the powders shown at the top of the page
Solubility rules
We often want to predict whether a precipitate will form when we mix two solutions. We can easily predict the products of a double displacement reaction by swapping the positions of the two negative ions.
The important point is that a precipitate must be insoluble. Some general solubility rules tell us which ionic compounds will not dissolve in water at room temperature. These are shown as solid (s) in the chemical equation.
Activation energy
Although they're useful, the diagrams above are missing something – the transition state between the reactants and the products. If we add this we can show that there are two energy changes in every reaction:
So all reactions absorb and release energy – whether they are exothermic or endothermic depends on whether more energy is released or absorbed overall.
The absorption of energy always comes first, to break the bonds in the reactants. So the resulting transition state always has more chemical energy than the reactants. The difference between the chemical energy in the reactants and in the transition state is known as the activation energy. It is energy that has to supplied from the environment before the reaction can happen.
Calorimeter
Used To determine if there is a relationship between the number of carbon atoms (or molar mass) of alcohols and enthalpy
Calorimetry is used to measure the energy absorbed or released as heat during a chemical change. The amount of heat energy released is calculated by measuring the change in temperature of a given quantity of water placed above the flame.
Steps for measuring the heat given off by combustion reactions:
A sample of known mass of substance is burned.
The energy generated by this reaction increases the temperature of water.
Initial and final temperature readings of the water are taken.
The change in temperature is used to calculate the energy evolved by the reaction as heat (q).
The amount of energy absorbed by the water in a calorimeter is given by the equation:
Rate of reaction
Fireworks displays rely on careful timing of a wide range of chemical reactions to produce their spectacular bursts of colour. Using reactions to our advantage often requires us to manipulate how slow or fast they occur. Some reactions are naturally faster than others but reactions can also be sped up or slowed down in different ways. As we have seen, some reactions are so fast that they cause explosions- which can be dangerous or controlled for things like rockets.
A rate is a measure of how quickly something changes. For example, speed is how quickly something changes position over time. The rate of a reaction is how quickly the reactants are converted into products.
