Question

1. for teks 13c, students must classify processes as exothermic or endothermic. which of the following is an endothermic process?

a. combustion of propane in a grill (δh < 0)
b. freezing of water to form ice (δh < 0)
c. melting of ice into liquid water (δh > 0)
d. neutralization of hcl by naoh (δh < 0)

1. a graph of enthalpy vs. progress of reaction shows reactants at 0 kj and products at -120 kj. this reaction is:

a. endothermic and absorbs 120 kj
b. exothermic and releases 120 kj
c. endothermic and releases 120 kj
d. exothermic and absorbs 120 kj

1. which example best aligns with teks 13d: \explain how factors affect energy changes in chemical reactions\?

a. changing the pressure of a gas during a reaction
b. changing the concentration of reactants and observing temperature change
c. observing the color change in a chemical reaction
d. measuring the ph change during titration

1. when you double the amount of reactant in a calorimeter experiment (assuming everything else constant) the temperature change will:

a. be half as much
b. be the same
c. double
d. become negative

1. if δh = +250 kj for a reaction, what can be said about that reaction (in terms of teks 13c/13d)?

a. it is exothermic and energy is released.
b. it is endothermic and energy is absorbed.
c. it is exothermic and energy is absorbed.
d. it is endothermic and energy is released.

Explanation:

• Question 5: Endothermic processes have $\Delta H>0$. Melting ice ($\Delta H > 0$) absorbs heat. Combustion ($\Delta H<0$), freezing ($\Delta H<0$), and neutralization ($\Delta H<0$) are exothermic.
• Question 6: $\Delta H=\text{Products}-\text{Reactants}=- 120\ kJ$. A negative $\Delta H$ means exothermic (energy released).
• Question 7: Changing reactant concentration (a factor) and observing temperature (energy change) aligns with TEKS 13D. Pressure (A) is less relevant, color (C) and pH (D) don't directly show energy - change factors.
• Question 8: Heat released ($q = mc\Delta T$) is proportional to reactant amount. Double reactant $\to$ double heat $\to$ double $\Delta T$ (if $m$ and $c$ constant).
• Question 9: $\Delta H=+250\ kJ>0$: endothermic (absorbs energy).

Answer:

1. C. Melting of ice into liquid water ($\Delta H>0$)
2. B. Exothermic and releases 120 kJ
3. B. Changing the concentration of reactants and observing temperature change
4. C. Double
5. B. It is endothermic and energy is absorbed.