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Flashcards in topic test three Deck (37)
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what is energy

the capacity to do work or cause change
- energy change: due to bond breaking / forming
- stored energy: due to attractive and repulsive forces between particles


what is a system / surroundings

- system: reactant and products
- surroundings: everything surrounding / outside of the system (not included in the reaction)


what is the law of conservation of energy

- states that energy cannot be created or destroyed
- can be transferred / changed from one form to another


What is bond breaking and forming

In nearly all reactions intermolecular and intramolecular forces/bonds are broken in the reactants to form new products


What is an exothermic reaction

- reaction that causes temperature of system to rise consequently heat flows out of the system (into surroundings)
- reacting system loses energy to the surroundings thus enthalpy decreases
- enthalpy change is negative


What is an endothermic reaction

- reaction that cause temperature of system to fall, consequently heat flows into the system (gains heat from surroundings)
- reacting system gains energy from surroundings thus enthalpy decreases
- enthalpy change is positive


what are physical changes

- involve breaking / making of weak bonds
- require small amounts of energy
- state changes (melting, boiling, freezing, dissolving, vaporisation)


what are chemical changes

- involves breaking / forming of strong chemical bonds
- large amount of energy is required
- when new products are being formed


what is enthalpy

- total energy present in the substance
- different reactions have different enthalpies as strength of bonds varies depending on each substance


what is the amount of enthalpy in a system

- the amount of energy released / absorbed by surroundings


what is change in enthalpy

- /\H is measure in kJ
- /\H = H(products) - H(reactants)


what is the transition state / activated complex

- maximum potential energy (Ep) in the reaction
- represents stage where bond breaking (endo) and forming (exo) occurs
- unstable and exists temporarily, once formed changes quickly to products or returns to reactants


what is the activation energy

- Ea: minimum amount of energy required for a successful collision which results in a reaction occurring
- referred to as Ea barrier which must be overcome for a reaction to occur


how does one measure rate of reaction

- amount of substance use or produced / time taken


what is the collision theory

- collision must occur for a chemical reaction to occur
- minimum specific amount of energy and favourable orientation is required for successful collisions


what are the factors affecting ror

- temperature: ^temp = ^kinetic energy of reacting particles and distribution of molecules (^velocity / movement / successful collisions / sufficient energy to overcome Ea)
- subdivision: ^SA (makes reactants smaller) = ^exposure to reactants / more collisions in given space (more successful collisions / Ea)
- nature: gases (more complex bond breaking / forming), solutions (no energy required to break intermolecular bonds)
- catalyst: provides alternate pathway with lower Ea (^successful collisions / sufficient Ea)
- concentration: ^c = ^ particles / collisions / Ea
- pressure: ^p = ^con. of particles (^ collisions / Ea)


explain the bonding involved in water

- covalent (intramolecular) bonds between H and O atoms
- weak dispersion forces (weakest intermolecular force) between water molecules
- hydrogen bonding (strongest intermolecular force, but still much weaker than covalent) between water molecules


what are dispersion forces

- polar: electrostatically attracted to other molecules (one side of the molecule being slightly more positive and the other slightly more negative)
- non polar: (no overall charge distribution) the molecules still need to be attracted to each other
- e are always moving: spend more time in one area than another, area becomes temporarily more -ve (other side temporarily more +ve)
- if non-p comes close to another molecule which has temporary +ve/-ve sides (dipole), temporary attraction occurs, happens throughout substance.


MP and BP of water

- MP: 0C
- BP: 100C, intermolecular forces (force between molecules) are broken, covalent bond holding H and O atoms together are not broken
- BP: is high compared to other molecular compounds (H bond is strongest intermolecular force)


surface tension as a property of water

- very high
- molecules are held together relatively strongly (H bonding occurring in all directions)
- surface layer there is no water molecules above to 'pull up' these molecules so the surface molecules tend to be pulled back into the liquid


density as a property of water

- liquid: cool water is denser than warm water, particles move closer tougher in a smaller amount of space
- solid: less sense than water, molecules slow right down, for, more H bonds which holds the, in an open hexagonal structure (prevents close packing)


what is solubility

- the extent to which a solute will dissolve in a solvent


polar and non polar solutes

- P: polar solute dissolves in polar solvent, are hydrophilic (water loving), dissolve in water
- NP: np solute dissolves in np solvent, are hydrophobic (water hating), don't dissolve in water


what are factors affecting solubility

- amount, nature, temperature, pressure of solvent / solute
- temp: solids and liquids (^temp = ^solubility), gases (decreased temp = ^ solubility)
- pressure: little affect on solids and liquids, decreased pressure of gas = decreased solubility


what are electrolytes

- a produces ions in a solution
- ionic substances dissociate (break down) to form ions
- covalent substances ionise (break down) to form ions
- strong: completely dissociate and partially ionise
- weak: partially ionise (double arrow)
- non: do not dissolve in water


what is concentration

- strong solution has more particles than a weak in the same amount of solvent
- [ppm] = m(solute mg) - m(solution kg)
- calculations: n=cV, m=cV, n=m/M


types of concentrated solutions

- unsaturated: contains less solute than it is able to dissolve at a given temperature
- saturated: contains as much solute as it can dissolve at a given temp / pressure
- supersaturated: contains more solute than a saturated solution under existing conditions
- stable/unstable: when temp changes some compounds release excess solute / some are stable and don't


what is an acid

- pH more than 7
- sour, turns blue litmus paper red, corrosive, conduct electricity, react with carbonate to form CO2, react with some metals to form H2, react with bases to form water
- common acids: HCl, H2SO4, H2SO3, CH3COOH, H2CO3, HNO3, NH4CO3, NH4NO3, C6H8O7, CH3CH(OH)COOH


what is a strong acid / weak acid

- strong: completely ionise to produce ions in solution
- e.g. HNO3 (nitric), H2SO4 (sulfuric), HCl (hydrochloric), HBr (hydrobromic), HI (hydroiodic) HClO4 (perchloric)
- other acids (weak): partially ionise (ethanoic, hydrofluroic, carbonic)


what is a base

- pH >7, taste bitter, turns red litmus paper blue, can be corrosive, conduct electricity, feel slippery, do not react with most metals, react with acids to form water
- common bases: NaOH, NH3, Ca(OH)2, NaHCO3, CaO, Na2CO3