Semester 1 Study Guide Essay

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Thermochemistry and
-read Ch. 10, just sections 10.3 and 10.5; pp. 317-318 # 24, 30, 32
energy: that which makes matter change -sound, fire, human movement, light, electricity -everything is either matter or energy system: reaction surroundings: everything outside of the reaction calorie: amount of E to raise one gram of H2O 1 C° -food Calorie=1 kcal=1000 calories joule: 1 cal=4.18 J exothermic: energy flows out of a system endothermic: absorbs energy from the surroundings specific heat: amount of energy required to change the temp. of 1 g of a substance by 1 celsius degree

-The unused matches have stored up energy-->POTENTIAL ENERGY (FROM THE POINT OF VIEW OF THE SYSTEM) -Energy is always from the system’s point of view
-Energy is either released into the surroundings or takes energy from the surroundings
-Kinetic Energy: energy due to motion -higher temp, molecules moving faster-->more K.E. -volume and pressure
-Water evaporating from your skin: H2O (l)-->H2O (g) -system gets energy from your body, so you get cold

-NaOH (s)Na+ (aq) + OH- (aq) + E
↑ ↑ ↑
Also part of surroundings-->only the concept of system
-Total energy is conserved
-Heat flow into surroundings results from a lowering of potential energy of the reaction system -in any exothermic reaction, some of the potential energy stored in the chemical bonds is converted to thermal energy (random kinetic energy) via heat.
-Heat required to change the temp. of a substance depends on: 1. amount of substance being heated (# grams) 2. temp. change (# degrees) 3. identity of substance
-calorie problems: -?g H2O 10°C to 11°C --> need 2 calories -?g H2O 10°C to 12°C (c=specific heat) Q=mc∆T 4cal=(2 g) (1 cal/g C°) (2 C°) -A hot piece of metal @ 90°C weighs 10.0 g. When placed in 30.0g H2O @ 10°C, the final temperature is 17°C. Find the specific heat of the metal. energy lost by metal=energy gained by H2O mmetal x cmetal x ∆Tmetal= mH20 x cH20 x ∆TH20 ↓ Final-Start (10.0 g) x (cmetal) x ((17-90)°C) = (30.0 g)(1.00 cal/g C°)((17-10)°C) cmetal = 0. 288 cal/ g C°

-enthalpy problems -System: -NaOH (s)Na+ (aq) + OH- (aq) + E ↓ (energy released into surroundings)

If gets, colder, then losing energy (E goes on left side in equation) -∆H > 0 if endothermic

Observations-see first few labs
Quantitative: having to do with #s
Qualitative: not #s
-be careful and descriptive
Types of Reactions-see wksht

1. Synthesis: making something A+B-->AB Ex: H2 (g) + 1/2 O2 (g) --> H2O (l) Ex: CaO (s) + CO2 (g) --> CaCO3 (s)
2. Decomposition: one on left; right has two or more things (breaking up) AB-->A+B Ex: HgO (s)Hg (l) 1/2 O2 Ex: NiCO3 (s) CO2 + NiO (s)
3. Combustion: reaction w/ O2 A + O2 --> you get the picture
Ex: 2 Fe (s) + 3/2 O2 (g) --> 1/2 Fe2O3 (s) -CARBON AND HYDROGEN COMBUSTION ALWAYS YIELDS CO2 & H2O Ex:CH4 (g) + 2O2 (g) --> CO2 (g) + 2 H2O (l) Ex: CH3OH (l) + 3/2 O2 (l) --> CO2 (g) + 2 H2O (l)
4.Metathesis/double replacement/double displacement
Ex: 2 NaCl (aq) + Pb(NO3)2 (aq) --> PbCl2 (aq) + 2 NaNO3
Ex: NaCl (aq) + AgNO3 (aq) --> AgCl (s) + NaNO3 (aq)
*Ex: CaCO3 (s) + 2 HCl --> CO2 + H2O + CaCl2
*CO2 + H2O is “H2CO3” --> carbonic acid (doesn’t exist)
5. Single displacement/ single replacement A+BC-->B+AC
Ex: Mg (s) + 2 HCl (aq)-->…