When speaking of change chemists refer to the system and surroundings together they make up the universe. you choose the stem that you want to investigate. when considering change you think whether the enthalpy and entropy are changing and how like when we stretched the rubber band compared to when we let it be slack if the system is an open system energy can pass between the system and the surroundings. a closed system is a system that is isolated from its surroundings and heart can neither enter nor leave. the law of conservation of energy states that energy cannot be created or destroyed. Gibbs free energy or delta G is a measurement that can be used to tell whether a change will occur spontaneously. Polymers (like rubber bands) are molecules mad of long strings of monomers that are attached to each other.
a Chemical reaction that continues to occur on its own once it begins is called spontaneous. Thermodynamics are used to answer the question ” can a reaction occur spontaneously like what we learned with delta S,H,G. Kinetics is used to answer the question ” how fast can a reaction occur. There are two factors that determine if a change can occur spontaneously.the first factor is if the change gives off heat when it occurs or absorbs heat when it occurs. (enthalpy) the second factor is if the change results in particles becoming more disordered or less disordered. (entropy) one way to show an enthalpy change is an energy diagram which is a diagram that shows the progress of the reaction from reactants to products along the horizontal axis. Endothermic is when the reaction absorbs energy exothermic is when the reaction releases energy. Activation energy is the energy necessary to break down the original bonds in order to form new ones. A catalyst is a substance that speeds up a chemical reaction without being used up itself.
Substances that dissolve in water to make solutions that conduct electricity are called electrolytes. Like how we tested mg which was conductive for a solution to conduct electricity there are two prerequisites. charged particles must be present and the charged particles must be able to move around. Some compounds dissolve in water to form charged particles called ions. The compounds are made of a positively charged metal ion and a negatively charged ion to balance the charge. Molecules that do not form ions in solutions are non-electrolytes. A battery is composed of two half cells like our copper and zinc half cells in the lab. the half where oxidation takes place is the anode. the half cell where reduction takes place is the cathode. the salt bridge is where negative ions go through to complete the circuit and keep everything balanced.
We examined the colors that make up visible light. We used a circuit with resistors to light up a single LED light. light is a form of energy known as electromagnetic radiation. that includes X-rays, ultraviolet, microwaves, and radio waves along with visible light. Light can be characterized by its wavelength and its energy. the wavelength of light is the distance between two corresponding points of a wave. All waves of light travel at the same speed in a vacuum. this speed is called the speed of light. the frequency of light is a property of wavelength and is used in the equation “speed of light=wavelength in meters X frequency in waves per second”. As wavelength increases, frequency decreases. the energy of light is related to the frequency and wavelength of the light. light that has a long wavelength has less energy than light that has a short wavelength. the wavelength of light determines if the light has enough energy to interact with the electrons in an atom. the outermost electrons are called the valence electrons these are the electrons that take part in chemical reactions. When an electron absorbs enough energy to be promoted to a higher state which called the excited state, to distinguish it form the ground state. A common process by which light is emitted from atoms or molecules is fluorescence which is what the LED gave off. A glow in the dark star (or glow tape) gives off light by a slightly more complicated process called phosphorescence.
metals are shiny or can be polished to shine. Metals also conduct electricity, so they’re used in electrical circuits, they conduct heat, can withstand high temperatures. Metals are also malleable. the majority of metals are more reactive than hydrogen. and are most commonly found in nature in ionic form, as positively charged ions involved in solid crystals or dissolved in water. Alchemists discovered some metals react more easily with most metal ion solutions than other metals do. reactions that occur between neutral metal atoms are called Oxidation-reduction reactions or “redox”. Oxidation is defined as giving up electrons and reduction is receiving electrons. We tested this with the the Hcl being dropped on Mg and copper and only Mg was affected by the Hcl. hydrogen is included with the metals even though its not one because it takes on the positive nature of a metal in its in strong acids. those acids are simple and convenient reagents which can quickly establish where an unknown metal stands in the series.
A mole is counting word used to count very large quants of very small objects. 1 mole= 6.022 x 10^23 a mole is like a dozen which we figure out in the lab is equal to 12. one mole of any single kind of atom or molecule is equal to its atomic mass. a molar mass is the atomic mass times however many atoms there is. 1 mole=22.4 L at STP which is standard temperature and pressure which well alway be using in our equations. the calculation of how many moles of reactants are needed to create a certain reaction is stoichiometry which is what we did today in class with the balloon and the baking soda and vinegar. in an equation you will need the molar mass of the substance, coefficients from the balanced equation, volume that one mole takes up. many times less than 100% of the expected product is found because there are many ways to lose small amounts of the product which is called percent yield.
In our lab we created CO2 gas that was supposed to inflate the balloon 6 cm however, that was not exactly accomplished. we used 4 different methods; baking soda and vinegar, seltzer water and heat, calcium carbonate and HCl, Calcium carbonate and heat. when matter undergoes change there often is a change in energy involved meaning energy will move from one place or form into another. if heat energy goes into something the chemical gains energy like the seltzer water and heat. if heat energy is released the chemicals lose energy. when you add energy to something the particles gain energy that gained energy goes into moving the particles faster. the extra energy could also change the bonds between the atoms or molecules. both attractive forces and bonds hold atoms or molecules together. it takes the input of energy to break weak intermolecular forces or chemical bonds. it takes less energy to break the attractive forces in holding molecules near each other in the liquid and solid phases. when attractions between molecules cause a phase change energy is given up and heat energy is released to the surroundings. an endothermic change is when heat is added to the reactants exothermic is when heat is released from the reactants. most changes also involve a change in how the tightly or loosely the particle are packed. the more loosely packed the more disorder there is the more tightly packed the less disorder there is. chemists call the disorder as entropy. which is symbolized by S.
Dyes are typically defined as organic molecules that bond directly to a textile to produce a color. in our lab we had the onion skins, the two teas, and carrot greens to create the dyes. the chromophore is that part of the dye molecule responsible for the color you see. the mordant assists in the building of the dye tot the textile. we soaked our strings in the mordants before we dipped them in the dyes. sometimes an autochrome will be present, which will modify the chromophore’s ability to absorb light energy. when dye is introduced, it forms an insoluble complex salt, sometimes called a lake, with the metal ion within the complex salt. while early dyes were obtained from natural resources, today nearly all dyes are produced synthetically.
the solid precipitates, which were the cloudy liquids, are insoluble compounds. our cloudy precipitates were the one that turned orange. when certain cations and anions are combined, water-insoluble ionic compounds may form. when these ions are in seperate aqueous solutions and then brought together, an insoluble solid, or precipitate forms. the precipitate is an ionic compound, or a salt, that forms because certain ions attract each other so strongly that they are removed from the water solution as the product of a chemical reaction. A double-replacement reaction is one type of precipitation reaction where a precipitate forms when one of the products is insoluble. Ions that do not precipitate in the reaction are called spectator ions. if you remove them from the total atomic equation they would form something called the net ionic equation.
If a substance contains water as part of its crystal structure it is called a hydrate. the solid that is left when the water is removed from the hydrate is called an Anhydrate. We had a hydrate in our lab in our clay pot. chemists used a measurement called a mole which counts the amount of atoms. A mole means 6.022×10^23. this called Avogadro’s number because he figured it out. the mass of one mole is equal to the number of carbon atoms in exactly 12g of pure carbon-12. chemists can use percent composition data to calculate a formula for an unknown compound. the empirical formula which is the formula for the smallest possible ratio of the elements. to find the percent composition simply add up the total mass of each element, and then the total mass of the compound. divide the total atomic mass of each element by the total mass of the compound and multiply by 100 to make it a percent.