Thermo chemistry
If ΔH is negative, is q always negative? Explain.
No — only at constant pressure
ΔH < 0 ⇒ exothermic ⇒ q(system) < 0
surroundings gain heat ⇒ q > 0
How to convert centigrade to Kelvin?
K = °C + 273.15
BaSO4 always written as ........
Solid
How to find grams from moles?
Multiply molar mass
Exothermic reaction → sign of ΔH?
Negative
–Which gas has greater density at same T and P: H2 or CO2
Higher molar mass ⇒ higher density
CO2
Spectators in BaCl2 + Na2SO4?
Na+ and Cl−
If pressure increases and temperature decreases, what happens to volume?
Both effects reduce volume
Name the 3 methods to calculate ΔH
q=mcΔT / bond energy / Hess’s law
What happens to pressure if the number of particles increases?
Pressure increases
If no precipitate forms, what is the net ionic equation?
No reaction (NR).
A gas mixture is 40% O2. Total moles = 5. How many moles O2?
2 moles.
q > 0 but ΔH < 0 — what does this mean?
q is for surroundings; system is exothermic
Why must temperature be in Kelvin?
Absolute temperature required
AgNO₃ + NaCl → write NET ionic (state matters)
Ag⁺ + Cl⁻ → AgCl(s)
You solve a gas problem and get negative moles. What is wrong?
Temperature likely not in Kelvin or sign error.
Same q added to water and metal → which has larger ΔT? Why?
metal (lower specific heat → larger ΔT)
You calculate n using PV=nRT but forget to convert mL to L. Result is too big or small?
Too big (volume too large numerically
NaOH + HCl → what type + net ionic
Neutralization
H⁺ + OH⁻ → H₂O(l)